iS3 



ELEMENTARY ANATOMY. 



LESS, 



down to complete abortion. A pelvic pair of limbs may be 

 developed without any thoracic ones, as in Bipes, Lialis, and 

 Ophiodes, and rudiments of the pelvic limbs may be the only 

 ones present, as in Python. 



10. The INNOMINATE BONE of man is one of the most 

 distinctive of his skeleton, distinguishable at a glance from 

 that of every other animal, widely differing even from that 

 of the Gorilla, which, however) much exceeds it in absolute 

 size. 



This large complex ossification, consisting as it does in man 

 of three primitive elements, presents three distinct bones in 

 lower animals the ilium, ischium, and pubis which, as in 

 man, meet to form the acetabulum. 



The fusion of these elements into this one bone is a 

 character which man shares not only with his own class, but 

 also with Birds. In Reptiles, however, we find three per- 

 manently distinct bones, whether or not they exactly corre- 

 spond with the three elements of the pelvis of man. 



The fusion of the two ossa innominata in a dorsal sym- 

 physis is a condition which sometimes occurs as in the 

 Ostrich. In that his ossa innomi- 

 nata are solidly attached to the 

 vertebral column, man agrees with 

 all Vertebrates above Fishes, with 

 the exception of Cetaceans and 

 some Lizards. In Fishes, however, 

 such a union is invariably absent, 

 and the ossa innominata are repre- 

 sented in them by ventral hard 

 parts only. 



The junction of the two ossa in- 

 nominata at a ventral symphysis is 

 a less constant character. Not only 

 is this junction entirely absent in 

 the class of Birds, with two excep- 

 tions (the Ostrich and the Rhea), 

 but in many Mammals (e.g. many 

 Bats, and Insectivora). 



The ventral union of the ossa 

 innominata with a simultaneous de- 

 tachment from the vertebral column exists in' Fishes, but 

 in no other Vertebrates, unless in some Reptiles with a rudi- 

 mentary pelvic structure. 



A detachment both from the vertebral column dorsally and 



FIG. 160. Pelvis of the small 

 Tanrec (Hemicentcte s), 

 showing the very elongated 

 ilia and the widely open 

 pubic symphysis. 



