36 



THE ANATOMY OF VERTEBKATED ANIMALS. 



are connected with, and supported by, a median membrane 

 bone which is closely connected with the ventral face of the 

 sternum. This is the interdavicula, freq'jantly called epister- 



fier- 



FlG. 13. — ^VenlTal view of the sternum and pectoral arches of Iguana tub&rtyuXaia. 

 letters as in i^g. 12. 



Th» 



The pelvic, like the pectoral, arch at iirst consists of a 

 simple continuous cartilage on each side, which, in Vertebrata 

 higher than fishes, is divided by the acetabulum, or articular 

 cavity for the reception of the head of the femur, into a dorsal 

 and a ventral moiety. 



Tliree separate ossifications usually take place in this car- 

 tilage — one in the dorsal, and two in the ventral, moiety. 

 Hence, the pelvic arch eventually consists of a dorsal portion, 

 called the ilium, and of two ventral elements, \\ie pubis ante- 

 riorly, and the- ischium posteriorly. All these generally enter 

 into the composition of the acetabulum. 



The ilium corresponds with the scapula. In the higher 

 Vertebrata the outer surface of the latter bone becomes di- 

 vided by a ridge into two fossas. The ridge, called the spine 

 of the scapula, frequently ends in a prominent process termed 

 the acromion, and with this, in Mammalia, the clavicle artic- 

 ulates. In like manner, the outer surface of the ilium be- 



