THE PELVIC ARCH. 



37 



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

 simple continuous cartilage on each side, which, in Verte- 

 brata 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. 



Three separate ossifications usually take place in this 

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

 Hence, the pelvic arch eventually consists of a dorsal por- 

 tion, called the ilium, and of two ventral elements, the pubis 

 anteriorly, and the ischiuTn posteriorly. All these generally 

 enter into the composition of the acetabulum. 



The ilium coiTCsponds with the scapula. In the higher 

 Vertebrata the outer surface of the latter bone becomes 



Fig. 14. 



Fipr. 14.— Side-view of the left Os innominatum of Man: //, ilium; 

 Is, ischium : Pb, pubis ; A, acetabulum ; Pp, Poupart's ligament. 



divided by a ridge into two fossae. The ridge, called the 

 spine of the scapula, frequently ends in a prominent process 

 termed the acromion, and with this, in Mammalia, the cla- 

 vicle articulates. In like manner, the outer surface of the 

 ilium becomes divided by a ridge which grows out into a 

 great crest in Man and other Mammalia, and gives attach- 

 ment to muscles and ligaments. 



The ischium coiTesponds very nearly with the coracoid 



