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THE LIBRARY OF THE

ZOOLOGICAL SERIES JUN 2 1938
F

FIELD MUSEUM OF NATURAL HISTORY

Volume XX CHICAGO, MAY 27, 1938 No. 30

NOTES ON THE ANATOMY OF THE TREESHREW
DENDROGALE

BY D. DWIGHT DAVIS
ASSISTANT CURATOR OP ANATOMY AND OSTEOLOGY

The recent researches of Clark, Gregory, and others have focused
a great deal of attention on the morphology of the treeshrews.
The fact that the Tupaiidae are now generally recognized as the
closest living relatives of the Primates has brought them within
the purview of those interested in the evolutionary history of man,
so that information regarding them is of more than ordinary interest.

There has been a tendency among many who have worked on the
morphology of these animals to lump all treeshrews together in the
two genera Tupaia and Ptilocercus, in spite of the fact that Lyon
(1913) in his extensive monograph of the family recognized no less
than six genera. Failure of non-systematists to give adequate
consideration to the remaining genera is probably due to their
rarity and to the fact that all bear a close superficial resemblance
to Tupaia. The results of the present study illustrate the inad-
visability of placing too much faith in external similarity when
dealing with survivors of decadent stocks.

The genus Dendrogale is one of the rarest of the Tupaiidae.
It includes the smallest members of the family. Fully adult indi-
viduals may have a body length of only 120 mm. Nothing is known
of their habits. The three specimens upon which the present study
is based were all shot from trees in broad daylight, and certain
features of the anatomy indicate that they are more arboreal than
Tupaia.

The stomach of the specimen dissected was distended with well-
chewed but undigested food. This material was examined by
Mr. W. J. Gerhard and Mr. Emil Liljeblad, entomologists of Field
Museum. It consisted, apparently exclusively, of fragments of
beetles of various types.
No. 415 383

384 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

The material for this study was collected by Dr. W. H. Osgood
in southern Annam, French Indo-China, in March and April, 1937.
It consisted of a complete skeleton of an adult male, a formalin-
preserved body of a slightly younger, but fully adult, male, and
study skins and skulls of a male and female. The individual from
which the skeleton was obtained was originally preserved entire
in formalin. Unfortunately the jar in which this specimen was
shipped was broken during transit and the animal arrived in a
completely desiccated condition. All efforts to resoften it having
failed, it was reduced to a skeleton. The species represented is
Dendrogale frenata Gray.

Despite the scanty material, it was decided that the rarity of
the genus and the interest that attaches to the treeshrews in general
warranted anatomical study. This decision has been more than
justified by the unexpectedly interesting nature of the results.

A complete skeleton of Tupaia belangeri concolor from Ban Me
Thuot, Annam, and a skeleton of Tana tana utara, without feet,
from Sandakan, British North Borneo, have been available for
comparison. Through the courtesy of the authorities of the United
States National Museum the following skeletons were also examined :
Tupaia javanica from Goenseng Boender, Java; Tupaia n. nicobarica
from Great Nicobar; and Tana t. tana (without feet) from Deli,
Sumatra. A rather poorly preserved specimen of Tupaia belangeri
modesta in alcohol was also used for comparison.

The drawings were made by Mr. John J. Janecek from original
sketches made by the author.

Especial acknowledgment is due Professor W. E. Le Gros
Clark. This study would have been virtually impossible without
his painstaking research on other tupaiids. His studies have been
constantly consulted, and the form of my presentation has been
largely guided by his accurate descriptions.

SKELETON

The skeleton is quite well known in Tupaia and Ptilocercus.
Since the skeleton of Dendrogale is essentially similar to that of
other tupaiids, detailed description seems unnecessary. The follow-
ing notes have been restricted to points that are of interest from
the comparative standpoint.

Skull. The skull of Dendrogale is quite well known. It was
figured and described briefly by Lyon (1913), who pointed out that
it is very similar to that of the short-nosed species of Tupaia. The

V-*0 * THE LIBRARY OF THE

1938 ANATOMY OF TREESHREW DAVIS 385

UNIVERSITY OF ILLINOIS

only conspicuous differences are the reduction of the large zygo-
matic fenestra found in Tupaia to a minute foramen in Dendrogale,
and the absence of palatal fenestrae. Both these characters are
shared by Ptilocercus.

A supraorbital foramen, which is absent in Ptilocercus, is present
and well developed in Dendrogale.

The brain case is somewhat more rounded, less angular, and

j? shorter antero-posteriorly than it is in Tupaia. This is true even

,Ljn fully adult individuals, a fact that Lyon was unable to determine

^because of lack of suitable material. A short sagittal crest is de-

^ veloped in old individuals, and the temporal crests are well defined

and rounded posteriorly, so that they take the form of a U. The

occipital crest is low but well developed.

Dentition. The dentition differs little from that of Tupaia.

The upper canine is two-rooted as in Ptilocercus, but lacks the small

basal cusp. This tooth has a single root in both Tupaia and Tana.

The third upper premolar is two-rooted. The fourth, which may

be two-rooted and without any evidence of a protocone in a few

species of Tupaia, is three-rooted and molariform in Dendrogale.

. The hypocones on the upper molars are reduced as compared with

{ Tupaia.

Vertebral Column. This region shows little of special interest.
' The vertebral formula is C7, D13, L6, S3, C27. In the cervical re-
gion a spinous process is present only on the axis and the seventh

> vertebra. The eleventh dorsal is the anticlinal. This is the same
L as Clark found in Ptilocercus, and contrasts with the tenth in the
r* three skeletons of Tupaia and two of Tana examined. The spines

on all the dorsals are about as well developed as in Tupaia. The
lumbars do not differ from those of Tupaia, except that the ana-

^pophyses and transverse processes are somewhat less prominent.

s The sacrum is composed of the usual three fused vertebrae. A
prominent spine is present on all but the first of these. Only the

> first segment articulates with the ilium; in this Dendrogale agrees
with Tupaia and contrasts with Ptilocercus where the first two

< sacral segments are in contact with the ilium.

Sternum. The sternum is not especially peculiar. The prester-

num is expanded anteriorly, with a rounded cephalic border, and
jj a cylindrical body posteriorly. The mesosternum consists of the
^customary five segments. The xiphisternum is about twice as long

as a mesosternal segment, and ends in a large, rounded cartilage.

386 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

Ribs. These bones are narrow as in Tupaia, not broad and
flattened as are those of Ptilocercus. There are thirteen pairs. Eight
pairs articulate directly with the sternum, two indirectly, and three
are floating.

Shoulder Girdle and Forelimb. The clavicle is similar to that of
other tupaiids. It is less curved than that of Tupaia, but somewhat
more so than that of Tana.

The scapula is slightly narrower than in other tupaiids. It is
more triangular in outline, the cephalic border not being rounded
as it is in Tupaia and Tana. As in other members of this family,
there is a distinct tubercle on the ventral border of the acromion
for the attachment of the deltoid muscle.

The deltoid crest on the humerus is not nearly so prominent nor
so long as it is in other tupaiids. The median epicondyle is much
less prominent, but there is a conspicuous entepicondylar foramen.
This foramen is absent in the skeleton of Tupaia belangeri examined,
but is present in the other two species of this genus and in both
specimens of Tana. The ulna and radius do not present any con-
spicuous peculiarities.

The carpus is strikingly similar to that of Ptilocercus. The
scaphoid and lunar are separate, instead of being fused into a single
bone as they are in Tupaia. Examination of the carpus in a study
skin of Tana tana shows that these bones are fused, as in Tupaia.
In keeping with the fused condition of the scaphoid and lunar in
Dendrogale the magnum articulates with the lunar, rather than with
the cuneiform.

Pelvis and Lower Limb. The pelvis resembles that of Tupaia
very closely, although it is somewhat more slightly built. The
ilia are spatulate. The symphysis is shortened, probably in cor-
relation with arboreal habits, as in Ptilocercus. The femoral process
in front of the acetabulum is much reduced as compared with Tupaia
and Tana. The pectineal eminence on the pubis is scarcely indicated.

The femur does not differ essentially from that of Tupaia. The
trochanter and lateral crest are somewhat less prominent, and the
head is set at a slightly less acute angle. The lateral crest on
the tibia is less developed and its border is more medial in position
than it is in Tupaia. The fibula is extremely slender and perfectly
straight. It is completely separate from the tibia. The tarsus is
like that of Tupaia, the calcaneum articulating with the cuboid.
According to Clark these two bones are completely separated by
the astragalus and the navicular in Ptilocercus.

1938 ANATOMY OF TREESHREW DAVIS 387

MUSCLES

The myology of both Tupaia and Ptilocercus has been fully
described by Clark. Although his descriptions are excellent, the
illustrations, particularly those accompanying his paper on Tupaia,
leave much to be desired. For this reason the myology in Dendro-
gale has been figured in some detail.

Unfortunately the muscles of the head, the lower limbs, and
most of the neck were destroyed before the specimen was preserved.
The rest of the body was in excellent condition, however, permitting
a very thorough dissection.

The arrangement of the muscles is, in general, similar to that of Tu-
paia, and in the present study comparisons have constantly been drawn
with Clark's description of the muscular anatomy of that animal.

MUSCLES OF THE THORAX
(Figures 49, 50, 52)

M . pectoralis major is very similar to the same muscle in Tupaia.
It is slightly overlapped posteriorly by the pectoralis abdominis and
the transversus abdominis, as noted by Clark in Tupaia. There
is no attachment to the clavicle. It inserts into the bicipital groove
of the humerus. The branch of the median anterior thoracic nerve
supplying it passes between the pectoralis minor and the pectoralis
abdominis, and not partly through the pectoralis minor as Clark
found in Tupaia.

M. pectoralis minor originates from the sternal ends of the fourth
to sixth sternal cartilages. No origin from the third, which Clark
found in Tupaia, was found. It inserts into the capsule of the
shoulder joint, beneath the deltoideus.

M. pectoralis abdominis (abdomino-humeralis of Clark) forms a
median raphe with its fellow from the opposite side at a point just
ventrad of the xiphisternum. The fibers converge and insert, partly
beneath but mostly lateral to, the insertion of the pectoralis minor
on the shoulder capsule.

M. subclavius is a small but well-marked muscle. It originates
from the sternal end of the anterior surface of the first costal cartilage.
There is no attachment to the rib itself, as Clark found in Tupaia.
The muscle extends obliquely forward and outward to insert on the
posterior and inferior surfaces of the distal half of the clavicle.
None of the fibers reach the coraco-clavicular ligament.

M. serratus anticus originates from the transverse processes of
the last four cervical vertebrae and the first eight ribs. The last

388 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

four slips interdigitate with the obliquus abdominis. The next one
forward emerges between the scalenus anterior and intermedius.
A few of the most ventral fibers of the scalenus anticus pass external
to it, instead of internal. The remaining anterior part of the muscle
emerges from beneath the scalenus anticus.

As in Tupaia, insertion takes place on the vertebral border of
the scapula. The fibers from the last four digitations converge to
insert on the inferior angle.

M. levator scapulae originates from the axis near its ventral
midline. Passing backward as a narrow band, its dorsal border
becomes almost inseparably bound to the ventral border of the
trapezius. It inserts on the coracoid process of the scapula as a
direct continuation of the insertion of the trapezius.

M. sternocostalis is narrow and poorly developed. It originates
from the ventral surface of the first costal cartilage, between the
origins of the scalenus posterior and the rectus abdominis. About
halfway back it thins out into an exceedingly thin aponeurosis
which inserts on the fifth costal cartilage near its sternal end.

MUSCLES OF THE SHOULDER GIRDLE AND UPPER ARM
(Figures 49-52)

M. trapezius. The anterior limits of the origin of the acromial
part of this muscle could not be determined because of the condition
of the specimen. The remainder of the origin does not differ from
that of Tupaia. It extends along the midline as far back as the
second thoracic vertebra. The origin of the spinous part extends
from here to the first lumbar vertebra. The two divisions meet in
a raphe over the scapular spine.

The acromial division inserts along the upper border of the
scapular spine, from the metacromion to its dorsal tip. The spinous
part inserts on the dorsal third of the lower border of the spine.

M. latissimus dorsi originates from the dorsal midline, beginning
just posterior to the spine of the scapula and extending back to a
point a few millimeters in front of the iliac crest. In the lumbar
region the muscle proper does not reach the midline, but is continued
toward it as a thin aponeurosis. As in Tupaia, there is no attach-
ment to the iliac crest or to the lower ribs. It is inserted into the
bicipital groove.

M. supraspinatus arises from the supraspinous fossa and spine
of the scapula. The muscle is partly divisible into two bellies.

390 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

The more superficial arises from the dorsal surface of the scapular
spine, the deeper belly from the supraspinous fossa. Both pass
under the acromion process to insert tendinously on the greater
tuberosity of the humerus.

M. infraspinatus originates from the infraspinous fossa. Its
lower half is concealed by the teres minor. It inserts by a stout
tendon on the head of the humerus, immediately behind the insertion
of the supraspinatus.

M. deltoideus arises from the anterior edge of the distal half of
the clavicle and tendinously from the ventral edge of the acromion
process. The acromial origin is much less extensive than that
figured by Clark for Tupaia, and is confined to a small tubercle on
the ventral border of the acromion. The fibers from these two
origins converge, giving a bipinnate form to the muscle, and insert
on the deltoid crest of the humerus. As in Tupaia the spinal division
of this muscle is absent.

M. teres major originates from the inferior angle and most of
the length of the axillary border of the scapula, and dorsally from
the fascia covering the infraspinatus. It inserts by a wide, flat
tendon into the lesser tuberosity of the humerus, beneath and
immediately posterior to the insertion of the latissimus dorsi.

M. teres minor originates aponeurotically from the fascia of the
infraspinatus. A very few of the fibers may arise from the medial
part of the scapular spine. It inserts tendinously on the humerus
close to the insertion of the infraspinatus.

Clark states that the teres minor conceals the infraspinatus com-
pletely in Tupaia. In Dendrogale, however, it does not extend
beyond the center of the scapula, so that much of the vertebral end
of the infraspinatus is not hidden.

M. spinohumeralis. Clark describes this muscle in Tupaia, but
does not mention it in connection with Ptilocercus. Its relations in
Dendrogale are much the same as in Tupaia.

M. subscapularis is a thick muscle originating from the sub-
scapular fossa. It is divided by four well-marked tendinous inter-
sections. The fibers converge, to insert tendinously on the lesser
tuberosity of the humerus, beneath and immediately behind the
insertion of the supraspinatus.

M. biceps arises by a long, stout tendon from the supraglenoid
tubercle. There is no short (coracoid) head, which Clark found in
both Tupaia and Ptilocercus. It inserts by a stout teridon into the
radial tubercle.

1938

ANATOMY OF TREESHREW DAVIS

391

M . coracobrachialis originates from the tip of the coracoid proc-
ess. As in Tupaia it is composed of two heads. The very small
short head originates non-tendinously beneath the origin of the long
head. It passes downward across the neck of the humerus to insert

Ct mast-i rCY occip

FIG. 50. Ventral body musculature. Superficial layer on the left, deeper
muscles on the right. XI.

on the inner lip of the bicipital groove, behind and mostly above
the insertion of the teres major. The long head originates tendi-
nously. Part of the fibers insert on the medial side of the shaft of the
humerus, immediately below the insertion of the latissimus dorsi.
The tendon, which runs the entire length of the muscle, continues
beyond this insertion to connect with a muscular insertion on the

392 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

median epicondyle and for a short distance on the shaft of the
humerus above it.

M. brachialis anticus is separable into medial and lateral heads,
as in Tupaia. The medial head arises from the anterior surface of
the shaft of the humerus below the deltoid crest. The lateral head
originates from the outer side of the shaft, from the level of the

Spinohum.

Lnfrasp.
Suprasp.

Tere.s minor

AcROMION
Suprasp.
Inffasp.

Trie. lot. (sup. head)
Deltoideus
Brack, ant. (La t head)

Trie lat _
(sup. head)

FIG. 51. Musculature of the shoulder and upper arm, lateral aspect. In
several of the muscles a section has been removed from the center in order to
expose underlying structures. X3.

distal end of the deltoid crest up to the insertion of the teres minor.
The two heads unite and insert by a single tendon into the coronoid
process of the ulna.

M. dorso-epitrochlearis,-2is in Tupaia, is composed of two heads.
One originates from the latissimus dorsi, while the other takes origin
in a similar way from the teres major, a few of the fibers originating
from the spinohumeralis. The two heads embrace the spinohumeralis
between them. The separate insertion of these two heads on the

1938 ANATOMY OF TREESHREW DAVIS 393

olecranon which Clark describes in Tupaia is not found in Dendro-
gale. The two heads fuse into a single mass which inserts by a
rather fine tendon on the medial side of the distal end of the olecranon.
M. triceps lateralis is composed of a superficial and a deep head,
as in Tupaia. The superficial head is a large muscular mass which
originates by a rather small tendon from the greater tuberosity of

Subscap

Doi-so - epitr
Coraco6rocA. (lonyhtatj)

ant (m*d head)
Biceps

FIG. 52. Musculature of the shoulder and upper arm, medial aspect. The
latissimus dorsi has been reflected to the left, and most of the dorso-epitrochlearis
and biceps have been removed. X3.

the humerus. Its origin is beneath the teres major, and immediately
above and behind the insertion of that muscle. The deep head is
very small, originating on the distal half of the shaft of the humerus.

As in Tupaia, the main mass of the muscle inserts on the proximal
end of the olecranon, while an aponeurotic expansion of the super-
ficial part inserts on the lateral border of the olecranon.

M . triceps longus originates by a short, stout tendon from the
infraglenoid tubercle and inserts on the posterior end of the ole-

394 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

cranon. It inserts tendinously on the extreme distal end of the
olecranon.

M. triceps medialis is apparently somewhat better developed in
Dendrogale than in Tupaia. It originates from the medial surface
of the shaft of the humerus as far up as the head, and inserts into
the proximal end of the olecranon.

M. anconeus is well developed and quite distinct from the triceps
medialis, contrary to what Clark found in Tupaia and Ptilocercus.
It originates on the median epicondyle and inserts on the proximal
end of the olecranon, hard by the insertion of the triceps medialis.

MUSCLES OF THE HIP
(Figures 49, 50)

M. psoas minor. The origin of this muscle is completely separate
from that of the psoas major. It arises from the first three lumbar
vertebrae. Just behind the third lumbar it becomes a wide, flat ten-
don, which inserts on the crest of the pubis, close to the symphysis.

M. psoas major arises from the lumbar vertebrae, from the third to
the sixth inclusive, and from the anterior part of the body of the
sacrum. It lies completely dorsal to the psoas minor. Insertion is
made on the lesser trochanter of the femur, immediately proximal
to the insertion of the iliacus.

M. iliacus is quite similar to the corresponding muscle in Tupaia.
It consists of the usual lateral and medial heads. The powerful
lateral head originates from the quadratus lumborum, although it
overlies that muscle broadly. The medial head is much less power-
fully developed, in contrast with what Clark found in Ptilocercus.
It arises from the iliac fossa and inserts, together with the lateral
head, on the lesser trochanter.

M. quadratus lumborum is much narrower than the iliacus, whose
wide lateral head hides it completely from the ventral side. It
arises by a tendon, considerably narrower than the tendon on the
psoas minor and almost hidden by muscle fibers, from the iliac
crest. There are adventitious origins from the tips of the transverse
processes of all the lumbar vertebrae. Insertion is made into the
transverse processes and sides of the bodies of the lumbar and last
four thoracic vertebrae.

M. sartorius arises from the central part of the inguinal ligament,
as in Ptilocercus. None of the fibers reach the pubic spine. It
inserts on the anteromedial surface of the tibia, immediately proxi-
mal to the insertion of the gracilis.

1938 ANATOMY OF TREESHREW DAVIS 395

M. glutens maximus arises from the whole anterior edge of the
iliac crest and from the lumbo-dorsal crest as far back as the end of
the sacrum. There is no origin from the sacral spines, which Clark
found in Tupaia. As in Tupaia the anterior fibers insert on the
fascia lata, and there is even an incipient separation between this
part of the muscle and the posterior part. The fibers from the
posterior part converge and insert tendinously on the third tro-
chanter of the femur. They are partly overlapped by the anterior
edge of the femorococcygeus.

Mm. gluteus medius and minimus do not differ greatly from the
same muscles in Tupaia. They are quite readily separable, contrary
to what Clark found in Tupaia. The medius is bilaminar. It arises
from the lateral surface of the dorsum ilii. As in Ptilocercus the
superficial fibers insert below those of the deeper division, which
inserts on the lateral aspects of the great trochanter. The minimus
originates along the ventral border of the dorsum ilii and inserts
tendinously on the anterior surface of the great trochanter.

M. gemellus is very similar to the corresponding muscle in Tupaia.
It originates from the margin of the sciatic notch and extends for-
ward to insert on the posterior surface of the great trochanter
together with the obturator internus. As in Tupaia it is a single
muscle.

M. piriformis does not differ from the corresponding muscle in
Tupaia.

Mm. obturatores are likewise like those of Tupaia.

M. quadratus femoris is a thin, triangular muscle layer which origi-
nates on the pubic arch in front of and deep to the semimembranosus.
It inserts into the posterior surface of the shaft of the femur.

M . femorococcygeus is wholly separable from the gluteus maximus,
its anterior edge overlapping that muscle from the origin down to
the insertion of the gluteus. It arises from the transverse processes
of the first three caudal vertebrae and extends the length of the
thigh, inserting into the thigh by a series of fleshy digitations from a
point immediately below the insertion of the gluteus maximus down
to the lateral surface of the lateral condyle, into the tendon of the
gastrocnemius, and into the fabella. The condition of this muscle
is very similar to that described by Clark for Ptilocercus.

MUSCLES OF THE THIGH

(Figures 49, 50)

M. semimembranosus arises, partly tendinously and partly by
fleshy fibers, from the ischial tuberosity immediately below the

396 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

origin of the biceps and from the posterior border of the ischium
almost as far forward as the symphysis. This exceedingly powerful
muscle inserts on the medial surface of the medial tibial condyle
just below the articulating surface and behind the internal lateral
ligament. A second much weaker tendon passes over the ligament
to insert on the condyle of the femur. This insertion is almost
identical with what Clark found in Tupaia, and differs considerably
from that of Ptilocercus.

M. semitendinosus originates by two heads, as in both Tupaia
and Ptilocercus. One is from the second and third caudal vertebrae,
beneath the femorococcygealis, and the other from the ischial tuber-
osity deep to the origin of the biceps. The two heads fuse a short
distance below their origin and extend across the thigh as a single
muscle. Insertion is made by a wide, flat tendon on the crest of the
tibia, immediately beneath the insertion of the gracilis.

M. biceps femoris arises by a tendon from the ischial tuberosity.
This muscle inserts by a wide fascial expansion into the outer sur-
face of the leg. This fascial expansion runs forward to the tibial
crest, and is a direct continuation of the fascia of the femorococcy-
gealis. None of the fibers reach the fibula.

M. tenuissimus originates from the fascia covering the dorsal
caudal musculature, immediately behind the posterior edge of the
gluteus maximus and beneath the femorococcygealis. In the
specimen dissected the tenuissimus does not reach the lower leg on
either side of the body, but is inserted aponeurotically into the inner
face of the biceps, near its posterior border.

M. rectus femoris arises by a single exceedingly stout and rather
wide tendon from the anterior inferior iliac spine only. There is no
origin from the margin of the acetabulum, and in this respect Dendro-
gale differs from both Tupaia and Ptilocercus. It inserts by a power-
ful tendon into the upper border of the patella.

M. vastus lateralis originates on the anterior aspect of the great
trochanter immediately below the insertion of the gluteus minimus,
as in Tupaia. The fibers of this large muscle converge and insert,
partly aponeurotically along the tendinous part of the rectus femoris,
partly aponeurotically on the lateral edge of the patella, and partly
on the quadriceps tendon.

M. vastus intermedius originates from the anterior, medial, and
lateral faces of the shaft of the femur for more than half its proximal
length. It inserts by a stout tendon into the upper margin of the
patella.

1938 ANATOMY OF TREESHREW DAVIS 397

M. vastus mediates. The origin of this well-developed muscle
extends along the anterior face of the upper quarter of the shaft of
the femur to a point on the anterior face of the great trochanter
deep to the origin of the vastus lateralis. It inserts into the medial
side of the quadriceps tendon and aponeurotically into the medial
border of the patella.

M. pectineus is a short, heavy muscle. It originates from the
front of the pubis, immediately lateral to the symphysis, and inserts
tendinously into the shaft of the femur immediately proximal to the
insertion of the adductor longus.

M. gracilis is a very broad, thin sheet of muscle. It originates
from the extreme medial end of the inguinal ligament and from the
whole length of the pubic arch to one side of the symphysis. It
inserts on the antero-mesial surface of the tibia, just distal to the
insertion of the sartorius.

M. adductor magnus originates from the central part of the
pubic ramus, from a point just in front of the origin of the semimem-
branosus forward about halfway along the symphysial border. As
in both Tupaia and Ptilocercus, there is no attachment to the tuber
ischii. It inserts on the posterior face of the femur, from the third
trochanter down to the popliteal region.

M . adductor brevis does not differ from the corresponding muscle
in Tupaia. It originates from the central part of the pubic arch,
lateral to the symphysis, and inserts into the posterior surface of the
shaft of the femur from the lower edge of the pectineus "to the
junction of the third and lower quarters of the femur."

M . adductor longus arises from the anterior end of the pubic arch
between the origins of the adductor brevis and the pectineus. It
inserts into the middle of the shaft of the femur. There is no apo-
neurotic expansion at its insertion, as Clark described for Tupaia.

RESPIRATORY SYSTEM

Larynx. This structure (fig. 53) differs in several details from the
larynx in Ptilocercus. There is no prominence on the thyroid carti-
lage for the attachment of the sternothyroid and thyrohyoid muscles.
The foramen for the exit of the internal laryngeal nerve is located
only one-quarter of the distance from the lateral border to the mid-
line of this cartilage, and it is approximately midway between the
anterior and posterior borders. A short superior cornu is present.

The epiglottis and cricoid and arytenoid cartilages do not differ
essentially from those described and figured by Clark for Ptilocercus.

398 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

The epiglottis is considerably larger, and the muscular processes on
the arytenoid cartilages are less prominent.

Trachea and Lungs. The trachea is composed of 20 incomplete
cartilaginous rings. The division into bronchi is similar to that of
Ptilocercus. The division and relation of the parts of the lungs are
also similar.

DIGESTIVE SYSTEM

All parts of the digestive system anterior to the pharynx were
removed with the head.

fpia/oitt.

-Thyroid cart:

cart.
Cricoid cart.

Trachea

FIG. 53. Dorsal aspect of the larynx. X6.

The Oesophagus is a straight, simple tube about 32 mm. long.

The Stomach (fig. 54, a) is purse-shaped, its vertical diameter ex-
ceeding its transverse diameter only slightly. In this respect it
differs rather widely from that of either Tupaia or Ptilocercus. In
general outline the stomach approaches that of Tupaia, but in the
development of the fundus and in the presence of a sulcus inter-
medius it resembles that of Ptilocercus.

The stomach wall is quite thin in the region of the fundus. It
becomes considerably thicker in the cardiac and pyloric regions, due
chiefly to the greatly increased thickness of the mucous layer at
these points.

Internally the mucous lining is thrown up into a series of very
prominent longitudinal ridges. These are wholly absent in the
fundus, are only moderately developed in the pyloric end, and are
most prominent in the cardiac region, where the mucous layer
greatly exceeds the muscular layer in thickness.

1938 ANATOMY OF TREESHREW DAVIS 399

The Small Intestine measures approximately 140 mm. in length.
As in Ptilocercus, the coils are not arranged in any definite order.
There is a rotation of the terminal part of this structure (fig. 54, 6)
similar to that described and figured by Clark for Ptilocercus.

The Colon is a straight, simple tube, not exceeding the small
intestine in diameter. It is approximately 27 mm. long (the anus
was removed with the skin). The ileo-colic junction is marked by
a faint constriction.

There is a well-developed Caecum (fig. 54, b) at the anterior end of
the colon. The neck is narrow, but the body of the structure is
expanded to about the diameter of the colon. In its normal position

Fundus
Oesophagus

Sulcus arxjularis

A ^ ^ Caecum

Colon

FIG. 54. a. The stomach, seen from the side. b. Junction of the small and
large intestines. The caecum has been reflected upward. X2.

the structure is reflected ventrally and caudally over the colon, and
its distal end is bent to the left upon itself.

The Liver (fig. 55) is in general similar to that of Ptilocercus, but
differs in a number of details. It has a breadth of 20 mm. and a
dorso-ventral diameter of 14 mm., thus differing considerably from
that of Ptilocercus, where these proportions are reversed. It is
divided into the usual three main lobes, the right lateral, central,
and left lateral, of which the central and left lateral are nearly
of equal size and the right lateral the smallest. There is no division
of the central lobe into right and left lobules except by the line of
the suspensory ligament, and this lobe forms scarcely more than
half of the diaphragmatic surface of the liver. The cardiac notch
is very shallow in contrast with the deep one found in Ptilocercus.

400 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

The fossa for the gall bladder is situated at the juncture of the
central and right lateral lobes, but most of the organ lies in a notch
in the central lobe. The caudate lobe on the posterior surface of
the right lateral lobe is larger than in Ptilocercus, and more dorsal in
position. The two processes on the right lobe which Clark homol-
ogizes with the Spigelian lobe differ considerably from the condition
in Ptilocercus. They are separated from the caudate lobe by a thin

Central lobe. Left lobe.

Gall bladde.

Right lobe

Caudate, lobe

Vena, caita infe-rior Spic/elian lobes

FIG. 55. Posterior surface of the liver. X3.

layer of the substance of the right lobe. The venous lobe is small and
rounded and projects caudally dorsal to the vena cava. The papillary
process resembles that of Ptilocercus, but is considerably larger.

The Gall Bladder and its ducts are similar to those of Ptilocercus.

The Pancreas is a large, irregularly shaped gland lying dorsal
to the stomach. The pars duodenalis is narrow. The superior
mesenteric vessels run through a deep notch in its cephalic border,
instead of piercing the gland as in Ptilocercus. The omental lobe
is very small. The pars linealis is narrow.

The Spleen is long and narrow. It lies in front and to the left
of the pancreas, above the cardiac end of the stomach. It is divided
into a series of irregular lobules by deep transverse fissures. The
anterior end of the organ bends abruptly toward the midline, giving
the whole structure the form of an inverted and reversed J.

MALE UROGENITAL SYSTEM

(Figure 57)

The scrotum, testicles, and part of the penis were removed in
skinning. The remainder of the urogenital system is well preserved,

1938

ANATOMY OF TREESHREW DAVIS

401

however, and supplies much interesting information when compari-
son is made with the corresponding structures in Tupaia and
Ptilocercus.

The Kidneys apparently are very similar to those of Ptilocercus.
The right is not situated higher than the left, however, as Clark
found to be the case in Ptilocercus. Each organ measures about
11 mm. long by 7 mm. wide. The anterior pole is broader than
the posterior.

The Prostate encircles the proximal end of the urethra, immedi-
ately below the mouth of the bladder. Superficially it appears
to be very similar to the corresponding organ in Ptilocercus, and
to differ considerably from the prostate in Tupaia.

i/rmaru bladde.

Urethra

Penis

CouJpers gland

FIG. 56. Proximal part of the male urogenital system, dorsal aspect. X3.

The Vasa Deferentia enter the urethra immediately below the
prostate and some distance above the seminal vesicles. This
contrasts sharply with the intimate relation that Clark found to
exist between the vasa and the vesicles in Ptilocercus.

The Seminal Vesicles agree quite closely with those of Ptilocercus.
Each is an elongate, slightly lobulated structure. A constriction
near the center of each organ probably marks the division between
the vesicular gland and the vesicular diverticulum which Clark
distinguished in Ptilocercus.

402 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

The absence of a Uterus Masculinus is noteworthy, as this struc-
ture is present and well developed in both Tupaia and Ptilocercus.

The Cowper's Glands are a pair of ovate, smooth-walled bodies
lying on either side of the urethra immediately behind the crus
penis. They open into the urethra by very short ducts.

Only the proximal half of the Penis is present, its tip having
been removed with the skin. It is a rather stout structure, firmly
attached to the ischio-pubic arch by well-developed Mm. ischio-
cavernosi. The M. levator penis attaches tendinously to its ventral
midline.

The Suprarenals are somewhat larger than those of Ptilocercus.
Each measures about 4.5 mm. in length. As in Ptilocercus, they
are bright yellow, ovate bodies lying against the kidneys, immedi-
ately above their hila.

DISCUSSION

It has generally been assumed that Ptilocercus occupies a rather
isolated position in the family Tupaiidae. This supposed isolation
is expressed by the usual practice of placing Ptilocercus alone in the
subfamily Ptilocercinae. This monogeneric subfamily is equivalent
in rank to the Tupaiinae, which contains all the remaining genera
of tupaiids.

The postcranial anatomy of Dendrogale shows that the great
superficial resemblance which this genus bears to Tupaia is mis-
leading. Not only does Dendrogale differ considerably from Tupaia
in fundamental anatomical characters, but it is noteworthy that
most of the differences are in the direction of Ptilocercus. Dendro-
gale, in other words, tends to bridge the gap that has been supposed
to exist between Ptilocercus and other tupaiids, and to occupy a
position somewhere between the two subfamilies. The characters
on which this opinion is based may be summarized briefly as follows:

The small size of Dendrogale is probably a primitive character.

Superficially the skull is very similar to that of Tupaia. It is
more primitive, however, in retaining the minute zygomatic fenestra
and in the absence of palatal fenestrae. Dendrogale shares both
these characters with Ptilocercus.

The dentition is somewhat less specialized, chiefly in the presence
of two roots on the canine and in the slight reduction of the molar
hypocones.

The anticlinal vertebra is the eleventh as in Ptilocercus, instead
of the tenth as in Tupaia and Tana.

1938 ANATOMY OF TREESHREW DAVIS 403

The ribs resemble those of Tupaia, but the expanded condition
of these bones in Ptilocercus is doubtless a secondary acquisition.

The sacro-iliac union agrees with Tupaia and differs from
Ptilocercus.

Dendrogale differs from both Ptilocercus and Tupaia in the
reduction of the median epicondyle on the humerus. This condition
probably represents a secondary specialization.

The scaphoid and lunar are not fused. A similar condition
obtains in Ptilocercus.

The shortened symphysis, a character which is shared by Ptilo-
cercus, may be a secondary adaptation to arboreal life.

The M. brachioradialis, which is absent in Ptilocercus, is present
in Dendrogale. Clark's suggestion that its absence is a primitive
feature is doubtful.

The absence of the short head of M. biceps is a primitive feature
not shared with either Tupaia or Ptilocercus.

The Mm. gluteus medius and femorococcygeus resemble those of
Ptilocercus rather than those of Tupaia.

The M. semimembranosus is like that of Tupaia, and differs
from that of Ptilocercus.

The condition of the M. tenuissimus seems to be one of secondary
degeneration, although its absence is primitive.

The form of the stomach is about midway between that of Ptilo-
cercus and that of Tupaia.

The liver is closer to that of Ptilocercus in the relative size of
its lobes, but the position of the gall bladder is as in Tupaia. The
relation of the gall bladder with reference to the liver lobes as found
in Ptilocercus is apparently the more primitive.

The colon, which Clark describes as "almost reptilian" in Ptilo-
cercus, is even less differentiated in Dendrogale.

The urogenital system is strikingly similar to that of Ptilocercus,
and correspondingly different from that of Tupaia. The complete
absence of a uterus masculinus is a curious condition which is not
easy to interpret, since it is present and well developed in both
Tupaia and Ptilocercus. The separation of the outlets of the vas
deferens and the seminal vesicles is also noteworthy. In general,
the urogenital system seems to be somewhat less specialized than
that of Ptilocercus.

Clark, as a result of his researches on Tupaia and Ptilocercus,
concluded that Ptilocercus is the most primitive of the treeshrews.

404 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XX

Tupaia, although showing many specializations of its own, would
then stand somewhere between Ptilocercus and the lemurs in the
evolution of the Primates. This view has not been challenged,
and is doubtless essentially correct. Dendrogale, however, shares
many of the primitive characters of Ptilocercus, without having
acquired its secondary specializations. The available evidence
indicates, therefore, that Dendrogale may be more primitive than
either Ptilocercus or Tupaia, and perhaps should occupy a place
at the bottom of the Primate ladder as far as living survivors of
the stock are concerned. These views, of course, may be modified
when the anatomy of the remaining tupaiid genera becomes known.

Lyon (1913, p. 36) concluded from a study of skins and skulls
of the tupaiids that Tupaia "is the most generalized member of
the Tupaiidae. ... It is easy to see how the other members of the
family with the exception of Ptilocercus have been derived by
relatively slight modifications from Tupaia." This opinion derives
no support from the present study. Tupaia, in spite of the great
speciation it has undergone and its wide geographic distribution,
is more highly specialized than either Dendrogale or Ptilocercus.

It is obvious that the subfamily Ptilocercinae of Lyon can no
longer be recognized, since the family Tupaiidae cannot now be
logically broken down into subfamilies.

REFERENCES
CLARK, W. E. LE GROS

1924. On the Myology of Tupaia minor. Proc. Zool. Soc. Lond., 1924, pp.

461-497.
1926. On the Anatomy of the Pen-tailed Tree-shrew (Ptilocercus lourii). Proc.

Zool. Soc. Lond., 1926, pp. 1179-1309.

1934. Early Forerunners of Man. A Morphological Study of the Evolution of
the Primates. Baltimore, Wm. Wood, xvi+296 pp.

GREGORY, W. K.

1910. The Orders of Mammals. Bull. Amer. Mus. Nat. Hist., 27, pp. 1-524.

KAUDERN, WALTER

1910. Studien iiber die mannlichen Geschlechtsorgane von Insectivoren und
Lemuriden. Zool. Jahrb. (anat.), 31, pp. 1-106.

LYON, M. W., JR.

1913. Treeshrews: an -Account of the Mammalian Family Tupaiidae. Proc.
U. S. Nat. Mus., 45, pp. 1-188.

L/BRARy