THE PECTORAL GIRDLE. 6oi 



The development of these parts in Teleostei has been recently investigated 

 by 'Swirski (No. 472) who finds in the Pike (Esox) that the cartilaginous 

 pectoral girdle is at first continuous with the skeleton of the fin. It forms 

 a rod with a dorsal scapular and ventral coracoid process. An independent 

 mass of cartilage gives rise to a praecoracoid, which unites with the main 

 mass, forming a triradiate bar like that of Acipenser or the Siluroids. 

 The coracoid process becomes in the course of development gradually 

 reduced. 



'Swirski concludes that the so-called pnecoracoid bar is to some extent 

 a secondary element, and that the coracoid bar corresponds to the whole of 

 the ventral part of the girdle of Elasmobranchii, but his investigations do 

 not appear to me to be as complete as is desirable. 



Amphibia and Amniota. The pectoral girdle contains a 

 more or less constant series of elements throughout the 



o 



Amphibia and Amniota ; and the differences in structure 

 between the shoulder girdle of these groups and that of Fishes 

 are so great that it is only possible to make certain general 

 statements respecting the homologies of the parts in the two 

 sets of types. 



The generally accepted view, founded on the researches of 

 Parker, Huxley, and Gegenbaur, is to the effect that there is a 

 primitively cartilaginous coraco-scapular plate, homologous with 

 that in Fishes, and that the membrane bones in Fishes are 

 represented by the clavicle and inter-clavicle in the Sauropsida 

 and Mammalia, which are however usually admitted to be 

 absent in Amphibia. These views have recently been challenged 

 by Gotte (No. 466) and Hoffmann (No. 467), on the ground of 

 a series of careful embryological observations ; and until the 

 whole subject has been worked over by other observers it does 

 not seem possible to decide satisfactorily between the conflicting 

 views. It is on all hands admitted that the scapulo-coracoid 

 elements of the shoulder girdle are formed as a pair of carti- 

 laginous plates, one on each side of the body. The dorsal half 

 of each plate becomes the scapula, which may subsequently 

 become divided into a supra-scapula and scapula proper ; while 

 the ventral half forms the coracoid, which is not always separated 

 from the scapula, and is usually divided into a coracoid proper, 

 a praecoracoid, and an epicoracoid. By the conversion of parts 

 of the primitive cartilaginous plates into membranous tissue 

 various fenestree may be formed in the cartilage, and the bars 



