Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/299/
MAIISUPIALI A. 
91 
behind the inner malleolus, and is inserted 
into the inner or tibial cuneiform bone. 
The muscle which has the relative position 
and origins of the flexor longus pollicis, sends 
its tendon by the usual route to the sole of the 
foot, where it divides and distributes a flexor 
tendon to all the toes except the rudimental 
hallux ; it has the same disposition in the 
Opossums, where the hinder thumb or great 
toe is fully developed ; for this modification, 
however, the Comparative Anatomist is already 
prepared by meeting with it in the first step 
from man, viz. in the Chimpanzee and Orang.* 
The third deep-seated muscle, being situ¬ 
ated internal to the two preceding ones, may 
be the analogue of the flexor digitorum commu¬ 
nis longus ; it nevertheless sends no tendon to 
the toes nor even to the tarsus, but its fibres pass 
from the tibia obliquely outwards and down¬ 
wards between the preceding muscle and the 
interosseous ligament to the fibula, where they 
are exclusively inserted so as to oppose the 
plantaris and rotate the foot outwards. This 
muscle closely adheres to the interosseous 
fascia, and thus resembles in its attachments 
the pronator quadratus of the fore limb : it is 
most developed in the pedimanous climbing 
Marsupials, where the rotation of the foot is 
more extensive and more useful. 
The subjoined illustration (fig. 113) of this 
modification of the muscles of the hind-foot is 
taken from a dissection of the Phalangista vul- 
pina, which very closely accords with that 
above described in the Dasyurus macrurus : a, 
expanded tendon of the sartorius; b, gracilis ; 
c, semitetidinosus ; and d, semi-membranosus ; 
both these muscles are inserted, as in many 
other quadrupeds, low down the tibia : e, gas- 
trocnemius; J\ plantaris; g, the analogue of 
the flexor longus pollicis pedis ; h, tibialis posti¬ 
cus ; this muscle divides and is inserted by two 
tendons, h' and h", into the internal and middle 
cuneiform bones : i, the rotator muscle of the 
tibia, probably a modification of the flexor 
digitorum communis pedis ; its fibres descend 
obliquely from the fibula p to the tibia t. 
In the muscles on the anterior part of the 
leg I observed no peculiarity worthy of notice ; 
the extensor brevis digitorum has, however, its 
origin extended into this region and is attached 
to the outside of the fibula. There are three 
peronei ; the external one is inserted into the 
proximal end of the fifth metatarsal : the ten¬ 
don of the middle peroneus crosses the sole in 
a groove of the cuboid like the peroneus longus : 
the internal peroneus is an extensor of the 
outer or fifth toe. The Percimeles lagotis, 
among the Saltatorial Marsupials, presents a 
different condition of the extensors of the foot 
from that above described. The gastrocnemii, 
soleus, and plantaris all arise above the knee- 
joint, and the tendon of the plantaris, after 
sheathing the tendo Achillis and traversing the 
long sole, is finally inserted into the base of 
the metatarsal bone of the fourth or largest 
toe ; thus this muscle, which is strongly de¬ 
veloped, bends both this toe and the knee, 
while it extends the foot. 
* Zoolog. Proceedings, 1830, p. 59. 
Fig. 113. 
Muscles of leg, Phalangista vulpina. 
Nervous System. 
The brain bears a smaller proportion to the 
body in the Marsupials than in any other order 
of Mammals: thus, in the Ursine Dasyure it 
is as 1 to 520, in the Wombat as 1 to 614, 
in the great Kangaroo as 1 to 800 : it is 
relatively largest in the smaller species of 
Petaurists and Phalangers. 
The Marsupial brain is also the simplest as 
respects its external form in the Mammiferous 
class. The cerebral hemispheres do not ex¬ 
tend over the cerebellum in any of the species, 
and in some, as the Dasyures and Opossums, 
they leave the optic lobes exposed. The brain 
consists, as in other Mammalia, of a medulla 
oblongata with a pons Varolii, cerebellum 
(d,flg• 114), optic lobes, or bigeminal bodies, 
(c, fig. 114), cerebrum (b), to which may be 
added, on account of their large proportional 
size and distinct development, the olfactory 
lobes (a, a,). In the Phalangers and Petau¬ 
rists, the Opossums, Perameles, the insectivo¬ 
rous Phascogales, and the smaller Dasyures the 
surface of the cerebral hemispheres is smooth 
and unconvoluted. In the Dasyurus ursinus 
the complication of the cerebral surface is 
merely indicated by a few slight indentations ; 
it is in the strictly herbivorous species as the 
Kangaroo (fig. 115) and Wombat, that the 
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