GREGORY, PRESEXT STATUS OF ORIGIX OF TETRAPODA 



oAi 



record, should be regarded as a highly modified archipterygiuni, especially 

 as the paired fins are identical in plan with the vertical fins. And yet 

 some authors {e. g.. Brans, 1901) have assumed that the paired fins of 

 Amia,, a much later and more specialized actinopterygian than Cheiro- 

 lepis, were of reduced archipterygial type. The point is important in 

 relation to the origin of the Tetrapoda, for if the early Actinopterygii 

 ever passed through an archipterygial stage they might be more closely 

 related to the Tetrapoda than is generally admitted. But none of the 



CX) 



B 



s.cl, supra- 

 ■if. scapula ; 



Fig. 4. — Pectoral girdle of Acipenser and Amia 

 {A) Arii.en.^er .sturio, after Goodrich, from Gegenbaur. (Bt Amia caha, from Good- 

 rich. Inner (medial) view of right side. 



Dermal elements: cc, clavicle ("infraclavicle") ; cl, cleithrum ("clavicle" i 

 cleithrum : p.f, posttemporal : ijo.cl, postcleithrum. 



Cartilage elements: (o, coracoid : m.c, mesocoracoid : (j1. articular surface: 



<l.c, dorsal cartilage. 



The sturgeons have the largest coracoscapula of any Actinopterygii : it is unossified : 

 the true clavicles are present and of large size. In Amia, as in more typical Actinop- 

 terygii, the coracoscapula mass is of relatively small size, this corresponding with the 

 relatively small size of the fin-muscles ; the coracoscapula is more or less ossified and 

 suturally divided into dorsal and ventral moieties named scapula and coracoid, respect- 

 ively ; tile true clavicles have disappeared, and the cleithrum is connected with the skull 

 by the stout supracleithrum and forked posttemporal. 



^arlv Actinopterygii show the least visible trace of ever having had widely 

 protruded basal elements in the paired or median fins : on the contrary 

 they emphasized the dermal rays and an undulatory movement of the 

 margins of the fin, rather than of its fleshy base. 



In the shoulder-girdle (Fig. 4) the Actinopterygii also developed the 

 dermal elements rather than the cartilaginous endoskeleton, the sturgeons 

 and their allies being the only ones with a large coracoscapula cartilage 

 (Fig. 4A). In most Actinopterygii the coracoscapula cartilage is small 



