122 Prof. H. G. Seeley. The Shoulder Girdle 



are similarly situate in both ordinal types, and similar in having a 

 scapular portion which extends vertically, and a precoracoid portion 

 which extends inward horizontally to the median line. On the other 

 hand, there is no close resemblance between these Orders in the 

 hones in question. (1.) The coracoids are dissimilar in form, and are 

 differently conditioned, for they do not meet in the median line in 

 any Chelonian, while there is no Sauropterygian in which they have 

 not a mesial union. (2.) In Mr. Hulke's figures it is only the 

 anterior portion of the ventral plate of the scapula which is lettered 

 as precoracoid. Thus the precoracoid does not enter into the humeral 

 articulation, or hold any position which theoretically can be com- 

 pared with the bone in Chelonia ; while the clavicular arch is anterior 

 to the supposed precoracoid in Sauropterygians, but holds no com- 

 parable relation in Chelonians. This latter difficulty apparently led 

 Mr. Hulke to regard the bones termed clavicular as omosternal in 

 Sauropterygia. But no Chelonian possesses an omosternum; so 

 that, if the identification were demonstrated, it does not support the 

 Chelonian hypothesis of the shoulder girdle. 



First, it may be observed that it is only in Anura that the precora- 

 coid enters the anterior margin of the glenoid cavity; but in TJrodela 

 the precoracoid appears to be excluded, so that it is not theoretically 

 impossible on an Amphibian hypothesis for the precoracoid to be 

 anterior to the acetabulum ; but the bone is always wedged between 

 the scapula and coracoid, and on the coracoid border the coracoid 

 foramen is always persistent, so that there is no analogy between 

 Urodele and Sauropterygian to sustain the identification of the pre- 

 coracoid which has been offered. Whenever two divergent bones 

 form the scapular arch those two bones are the coracoid and scapula ; 

 but there is no analogy to support the hypothesis that the precoracoid 

 might form the free extremity of the scapula, as in Mr. Hulke's figure 

 (loc. cit.). There is no conclusive evidence of the mutual relations of 

 the scapulo-precoracoid to the glenoid cavity in the Chelonia, but, 

 unless it could be shown that the relations of these bones to the 

 shoulder girdle were the same in both types, Chelonian analogy with 

 Sauropterygia in this part of the skeleton rests upon an inconclusive 

 basis of fact. In Chelonians the ascending process of the scapula 

 extends dorsally towards the vertebrae, while in Sauropterygia it 

 extends backward above the glenoid articulation for the humerus, 

 and there is no evidence that these structures are homologous. 



If the evidence is insufficient to sustain the interpretation discussed, 

 it is found that the precoracoid has disappeared as a separate element 

 from the skeleton in Lacertilia, and in most existing Ornithomorpha 

 {'Roy. Soc. Proc.,' vol. 49, p. 520). It is recognised in association 

 with the coracoid in certain Birds ; and the persistence of the coracoid 

 foramen gives some evidence that the precoracoid is not unrepre- 



