2T,2 



VERTEBRATE SKELETON 



while all but universally the pectoral halves are connected in the 

 middle line. 



Fig. 



244. — A, pectoral and B, pelvic fins of Cladoselache (Dean, '94). b, basalia; 



r, radialia. 



The Devonian shark Cladoselache (fig. 244) presents a primitive 

 condition. Its pelvic fin contains a series of radialia, strikingly like 

 those of a median fin, some being in line with rod-Hke 

 basalia, others connected with larger elements, appar- 

 ently fused basalia. The anterior basals of the two 

 sides approach each other in the midventral line and 

 only need to meet to form the ischio-pubic bar of a 

 true girdle. The fusion of the basalia of the pectoral 

 girdle has gone farther, but the two halves have not 

 met. Chlamydoselachus (fig. 245) has the basalia of 

 the pelvic fin fused to a long puboischium, perforated 

 by several nerves, the foramina possible indications of 

 the compound character of the cartilage. With this 

 pelvis a number of radialia are connected directly; 

 those farther back are articulated to two elongate 

 cartilages (fused basalia of this part of the fin), form- 

 ing a basipterygium. 



ELASMOBRANCHS. — The pectoral girdle of 

 most Elasmobranchs is U-shaped (fig. 242). The 

 glenoid surface (usually a ridge) separates scapular 

 and coracoid regions which afford origin for the fin 

 muscles. The supracoracoid foramen is near the 

 ridge and in Raiaj (fig. 246) the nerve divides within it, emerging on 

 the outer surface by two foramina. The scapular part extends far up 



Fig. 245. — Half 

 of pelvis and pel- 

 vic fin of Chla- 

 tnydosclachus 

 (Goodey, 'lo). b, 

 basipterygium; p, 

 pelvis with nerve 

 foramina. 



