FISCHEE ON THE PELYIS OF THE MAMMALIA. 17 



bone without a distinct termination. Perhaps it is not to be wondered at, 

 that the same abdominal pouch, which had hitherto been noticed only in the 

 genus didelphis, has lately been detected in a species of New Holland Bat, 

 since this genus has such distinct spines of the os pubis. The skin seems to 

 gape in these species between the spines, as it does in the human monstrosi- 

 ties, in whom the bones of the pubis gapes, being united by no symphysis ; 

 as likewise happens to those with hare lips, in whom the maxillary bones 

 are not united ; the skin of the head is also wanting in those foetuses, in which 

 a great portion of the vault of the cranium is deficient. Since it so happens 

 that in almost all animals the teats are placed in the lower part of the abdo- 

 men, it may be the more readily comprehended why they are placed in the ab- 

 dominal pouch. Nevertheless, all these considerations offer no sufficient ex- 

 planation of the peculiarities in the structure of the internal genital organs in 

 the didelphis. 



Very broad, slender, and almost papyraceous ascending and descending 

 rami of the os ischium still further distinguish the pelvis of the vespertilio 

 murinus ; like that large osseous lamina in the situation of the manubriuin of 

 the sternum, and like the broad osseous terminations of the inferior ribs at 

 their sternal extremities. The foramen ovale is very small, but truly oval ; the 

 conjugate diameter is very long and oblique ; the bones of the ilium, elongated 

 and linear, are inclined backwards, triangular, with margins slightly winged ; 

 of the three surfaces of this bone, the anterior is the only one between which 

 the bodies of the sacral vertebrae project ; the other posterior is internal, the 

 third posterior external. The symphysis of the pubis is very short ; the de- 

 scending branches of this bone, and the ascending ramii of the ischium, proceed 

 as in man. Between those branches the inferior aperture of the pelvis is 

 narrow, perhaps in the male, but the greater pelvis, always broader, ascends 

 backwards, covered only by the very narrow sacrum and the still narrower os 

 coccyx, or perhaps rather longitudinally divided into a right and a left portion. 

 The anterior coccygeal vertebrae have very short and broad transverse processes, 

 cut short at the apex and the margins almost running together ; the vertebras 

 of the distinct portion of the tail are elongated, very slender and simple. The 

 pelvis viewed generally, with a reference to the thorax, is very small ; can it 

 be that the pelvis of the female bat is so narrow, lest the weight of a broader 

 pelvis should interfere with her flight ! or, that the mother may more easily 

 carry along with her in her flight the young, adhering to the jjiammge upon 

 her broad breast ? also; in a manner, as the young of the didelphis born in an 

 imperfect state, are finally developed after birth, whilst adhering to the 

 mammse. Autenreith. 



Section 16. 5. Glire*. Rodentia, or Gnawers. In very many rodents the 

 os sacrum is composed of three vertebrae, as in the common mouse, the rat, 

 the woodmouse, the common squirrel, &c. ; four in the hare, the 

 guinea-pig, the aguti, and the crested porcupine ; five in the alpine marmot, 

 and in the beaver. In this order of the mammalia the lumbar vertebrae pass 

 gradually into the sacral, and the sacral into the coccygeal. The posterior 

 portion of the os sacrum is somewhat more slender than the anterior, yet in 

 some, as in the mouse, both portions have the same breadth. 



Section 17. In this natural family of animals, the coccygeal vertebra are 

 numerous ; the guinea-pig has six, the crested porcupine ten, the hare sixteen 



