356 



ANATOMY OF VERTEBRATES. 



226 



fig. 226, 62. In the Kangaroos and Potoroos the eye is arrested 

 by a strong process given off from near the middle of the ilio- 

 pubic ridge, and this process may be ob- 

 served less developed in the other Mar- 

 supialia. The tuberosity of the ischia 

 inclines outward in a very slight degree 

 in the Dasyures, Oj^ossums, Phalangers, 

 Petaurists, and Perameles, in a greater 

 degree in the Kangaroos and Potoroos, 

 and gives off a distinct and strong obtuse 

 process in the Wombat, fig. 226, 63, which 

 not only extends outward but is curved 

 forward. In the Potoroos the symphy- 

 sis of the ischia, or the lower part of 

 what is commonly called the symphysis 

 pubis, is produced anteriorly. The length 

 of this symphysis, and the straight line 

 formed by the lower margin of the ischia, 

 is a characteristic structure of the pehds 

 in most of the Marsupials. 



The marsupial bones, figs. 226,227, 7n, 

 are elongated, flattened, and more or less 

 curved, expanded at the proximal extre- 

 mity, which sometimes, as in the Wombat, 



Right OB innominatuni and marsupial ^g articulatcd tO thc pubis bv tWO polutS I 



boue. Wombat. , . 



they are relatively straightest and most 

 slender in the Perameles ; shortest in the Myrmecobius, where they 

 do not exceed half an inch in length ; longest, flattest, broadest, and 

 most curved in the Koala, where they nearly equal the iliac bones 

 in size. They are always so long that the cremaster muscle winds 

 round them in its passage to the testicle or mammary gland, and 

 the uses of these bones mil be described in treating of that 

 muscle. Homologically they are the last pair of lumbar hsema- 

 pophyses advanced, as in many Reptiles, from the sclerous to the 

 osseous states : teleologically they belong to the category of the 

 trochlear ossicles, commonly called sesamoid, and are developed in 

 the tendon of the external oblique which forms the mesial pillar 

 of the abdominal ring, as the patella is developed in the tendon of 

 the rectus femoris. I cannot, however, participate in the opinion 

 of Laurent and De Blainville,* that the marsupial bones are super- 

 added to the abdominal muscles to aid in an unusually energetic 



' 'Bulletin des Sciences Medicales' of Ferussac, 1827, No. 77, p. 112, and the 

 ' Annales d'Anat. et de Fhysiologie,' 1839, p. 240.* 



