PECTORAL AND PELVIC GIRDLES 



241 



Crossopterygii and Chondrostei an infraclavicle or clavicle proper, 

 while one or two " post-clavicles " may be present in relation with 

 the hinder margin of the cleithrum. The infraclavicles, or in 

 their absence the cleithra (e.g. Holostei and most Teleostei), 

 usually meet in a median ventral symphysis, so that the secondary 

 girdle tends to acquire the characteristic hoop-like arrangement 

 of its parts which has been lost in the primary girdle. With 

 the development of a bony secondary girdle, the primary girdle 

 (scapula and coracoid) becomes much reduced, and, as a rule, 

 does little more than connect the fins with the cleithra. 

 The secondary girdle acquires a dorsal connexion with the skull 

 on each side by means of the 

 post -temporal bone, which is 

 attached below to the supra- 

 clavicle and above to the periotic 

 capsule. In the Chondrostei 

 and the Dipnoi the primary 

 girdle retains its primitive carti- 

 laginous condition, but in the 

 Crossopterygii, Holostei, and in 

 all Teleosts it is ossified as dis- 

 tinct scapulae and coracoids. To 

 these may be added in some 

 Teleosts a mesocoracoid formed 

 by a separate ossification of the 

 coracoid cartilage (Fig. 143). 1 



With the possible exception 

 of small paired or median carti- 

 lages inserted between the inner 

 extremities of the basipterygia 

 in Polypterus and a few other 

 Teleostomi, the pelvic girdle is absent in all the existing members 

 of this group, having either become completely suppressed, or 

 remaining unseparated from the basipterygia of the pelvic fins. 2 

 In the Dipnoi (Fig. 144) there is a true pelvic girdle which has 

 some points of resemblance to that of certain of the caudate Am- 

 phibia. It is represented by a median, lozenge-shape, cartilaginous 



1 It is more probable that in most existing Teleostomi the pelvic girdle has 

 undergone complete suppression, in which case these cartilages are vestiges and 

 not rudiments. 



2 See, however, Goodrich, Quart. Journ. After. Sci. xlv. 1901, p. 311. 

 VOL. VII R 



FIG. 144. Ventral view of the pelvic girdle 

 of Protopterus. a, Prepubic process ; 

 b, lateral process for the fin ; c, epipubic 

 process ; (jr, ridge for the origin of the 

 tin muscles ; HE, skeleton of the 

 fin ; J/, myotomes ; J/', myoconimata. 

 (From Wiedersheim. ) 



