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/lit29464/295/
MARS UPI ALI A. 
287 
In the Peophagous Marsupials no rudiment 
of the innermost toe exists. The power of the 
foot is concentrated in all these genera on the 
fourth and fifth or two outer toes, but especially 
the fourth, which, in the Great Kangaroo, is 
upwards of a foot in length, including the 
metatarsal bone and the claw. This formidable 
weapon resembles an elongated hoof, but is 
three-sided and sharp-pointed like a bayonet, 
and with it the Kangaroo stabs and rips open 
the abdomen of its assailant : with the ante¬ 
rior extremities it will hold a powerful dog 
firmly during the attack, and firmly supporting 
itself behind upon its powerful tail, deliver its 
thrusts with the whole force of the hinder 
extremities. 
The cuboid bone which supports the two 
outer metatarsals is proportionally developed. 
The internal cuneiform bone is present, though 
the toe which is usually articulated to it is 
wanting. It is also the largest of the three, 
and assists in supporting the second metatarsal ; 
posteriorly it is joined with the navicular and 
external cuneiform bones, the small middle 
cuneiform occupying the space between the 
external and internal wedge-bones and the 
proximal extremities of the two abortive meta¬ 
tarsals. The great or fourth metatarsal is straight 
and somewhat flattened ; the external one is 
compressed and slightly bent outwards ; the toe 
which this supports is armed with a claw simi¬ 
lar to the large one, but the ungueal phalanx 
does not reach to the end of the second pha¬ 
lanx of the fourth toe, and the whole digit is 
proportionally weaker. 
In the climbing Potoroos, (Hypsiprymnus 
ursinus and Hypsiprymnus dorcocephalus), the 
two outer toes are proportionally shorter than 
in the leaping species, and are terminated by 
curved claws by which they gain a better hold 
on the branches and inequalities of trees. 
Myology.— To give a description of the 
muscular system with the same detail as of the 
osteology of the Marsupials would not be at¬ 
tended with the same advantages. Modified 
as this system necessarily is in conformity with 
the various modes of locomotion in the different 
Marsupial genera, as running, leaping, burrow¬ 
ing, swimming, even flying, we should here 
fail to detect in these modifications so many 
marks illustrative of the aberrant and inferior 
type of structure of our present group as we 
have witnessed in those of the skeleton. In 
addition, moreover, to their physiological rela¬ 
tions, the importance of the passive and endur¬ 
ing parts of the locomotive system to the 
zoology both of recent and extinct species, con¬ 
fers upon them a claim to our attention which 
the more perishable though more highly organ¬ 
ised and active parts of the same system do not 
possess, even if a detailed myology comported 
with the scope and extent of the present work. 
The present notice, therefore, of this depart¬ 
ment of the anatomy of the Marsupialia will 
be limited to a brief description of a few of the 
most striking peculiarities. 
Every one knows that the erect position is 
the most usual one in the Kangaroos ; yet the 
conditions of this posture are very different from 
those in the human subject. The trunk, in¬ 
stead of resting on two nearly vertical pillars 
so placed with reference to the superincumbent 
weight that it rather inclines to topple forwards, 
is here swung upon the femora as upon two 
springs, which descend from the knee-joints ob¬ 
liquely backwards to their points of attachment 
at the pelvis ; and the trunk is propped up be¬ 
hind by the long and powerful tail (fig. 103). 
In Man the massive and expanded muscles 
which find their attachment in the broad bones 
of the pelvis, especially at the posterior part, 
are the chief powers in maintaining the erect 
posture. But in the Kangaroo the glutei offer 
no corresponding predominance of size; the 
narrow prismatic ilia could not, in fact, afford 
them the requisite extent of fixed attachment. 
The chief modifications of the muscular sys¬ 
tem in relation to the erect position of the trunk 
in the Kangaroo are met with on the anterior 
part of the base of the spinal column. The 
psoœ parue, for example, present proportions 
the very reverse of those which suggested their 
name in human anatomy. They form two thick, 
long, rounded masses, which take their origin, 
fleshy, from the sides of the bodies and base of 
the transverse processes of the lower dorsal and 
all the six lumbar vertebrae, and from the extre¬ 
mities of the three last ribs ; the fibres converge 
penniformwise to a strong, round, middle 
tendon, inserted in the well-marked tubercle or 
spine of the pubis, already noticed. 
The disposition of the abdominal muscles, 
especially at the pubic and hypochondriac re¬ 
gions, has been described and figured by Mr. 
Morgan* and Professor Vrolikf in the female 
Kangaroo. The principal modifications are 
seen first in the presence of a large muscle 
called the triangularis by Tyson, the anterior 
rectus abdominis by Mr. Morgan,J and con¬ 
sidered as the analogue of the pyramidalis 
muscle by Meckel ; secondly, in the equal de¬ 
velopment of the cremaster in both sexes ; and 
thirdly, in the formation of a moveable bone in 
the situation and, as it were, in the substance 
of the mesial or internal pillar of the abdominal 
ring, which bone serves as a trochlea or pulley 
for the cremaster, and affords an extensive 
attachment to the abnormally developed pyra¬ 
midalis. 
This part of the muscular system is here 
described as it exists in a male Phalanger (fig. 
112), that sex being chosen, because most of 
the peculiarities, as the extensive pyramidalis,§ 
the cremaster, and the ossified tendons of the 
external oblique abdominal muscle have been 
regarded as being essentially connected with the 
physiology of the marsupial pouch, whereas 
they are equally developed in both sexes. 
The external oblique (obliquas ext emus), 
besides the usual origin by digitations from the’ 
ribs, also arises from the fascia lumborum ; it 
is inserted fleshy into the summit of the mar- 
* Linn. Trans, xvi. 1833. 
f Tydschrift voor de Natural, 1837. 
f A portion of the external oblique is included 
by Mr. Morgan with the triangularis under this term. 
§ Considered by Home as a sling by which the* 
mammae were supported.
        

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