SKELETON. 105 



The Shoulder Girdle. 



FISHES. The pectoral or shoulder girdle in the elasmobranchs is 

 more or less U-shaped, the bottom of the arch crossing the ventral 

 surface between the skin and the peritoneal membrane, this ventral 

 portion being known as the coracoid region, which is limited dorsally 



FIG. 108. Diagram of girdles and appendages from the posterior side; upper letters, 

 fore limb; lower, hind limb, a, acetabulum; c, carpus; co, coracoid, /, femur; fi, fibula; 

 g, glenoid fossa; h, humerus; U, ilium; is, ischium; me, ml, metacarpals, metatarsals; p, 

 pubis; pc, procoracoid; ph 1 - 3 , phalanges; r, radius; s, scapula; u, ulna; 1-5 digits. 



by the point of attachment (glenoid fossa) of the fin. Dorsal to the 

 fossa is the scapular region. Not infrequently the dorsal part of 

 the scapular region is segmented off as a separate suprascapula. 



FIG. ioq. Pectoral girdle and cartilaginous fin skeleton oiScyllium. c, coracoid region; 

 gl; glenoid surface; ms, mesopterygium; mt, metapterygium; p, propterygium; r, radialia: 

 s, scapular region. 



The girdle is usually free from the axial skeleton, but in the skates 

 (raiae) the suprascapula articulates with the adjacent vertebrae. 



In the simpler teleostomes (some ganoids, dipnoans) the cartilagin- 

 ous girdle is reinforced by membrane bones derived from the skin. 



