MARSUPIALIA. 



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 (Jig. 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 l\\e gluttei 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 

 psoa parva, 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 ubdominis by Mr. Morgan,} 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 (jig. 

 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 (obliquus externus), 

 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. 



t Tydschrift voorde Natural, 1837. 



j 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. 



