Mr. J. W. Hulke. On the Shoulder Girdle 



and I do not find any fault with those authors who use these names 

 indifferently as synonyms of a certain piece in the secondary 

 shoulder girdle. I prefer, myself, the term interclavicle, since Gotte's 

 embryological investigations have appeared to demonstrate that the 

 piece thus denoted is a derivative of the mesial ends of the clavicles. 

 For the analogous part in the Amphibian girdle, since W. K. Parker 

 apparently demonstrated its origin from the epicoracoids (and, if so, 

 it is not the morphological equivalent of the Lacertilian interclavicle), 

 I prefer his name omosternum, which has the convenience of imply- 

 ing its essential difference from the iuterclavicle. 



In Plesiosauria the (primary) shoulder girdle, as is well known, 

 consists of a dorsal and of two ventral rays, the fossa glenoidalis being 

 seated (approximately) at the spot whence the three rays diverge. In 

 addition to these component parts there are others which, for reasons 

 to be presently stated, I have suggested are omosternalia ; if such 

 they are also parts of the primary girdle. 



Sc. 



(Hulke) 



Sc(Seeley) 



Cor. 



FIG. 8. Left half of primary shoulder girdle of Plesiosaurus cliduclius (Seeley). 

 From photograph of specimen in Woodwardian Museum ; taken June, 1869. 



Professor H. G-. Seeley, however, finds, in these parts, clavicles and 

 interclavicle, a view which, if established, places them in the 

 secondary girdle.* 



Concerning the posterior ventral ray, the suggestion that it may 

 include the coracoid and also the precoracoid element has, I think, 

 never been seriously argued, and I believe that all comparative 

 anatomists now agree in regarding it in its entirety solely as coracoid. 



After the recognition of " the large flat bone," by Buckland, as 

 the " sternum " in Ichthyosaurus, and after its correspondence to the 

 coracoid in Crocodilia had been shown by Conybeare, the latter's 

 lenhfication of the Plesiosaurian coracoid, when soon afterwards 

 this Sauropterygian was discovered by him and De la Beche, almost 

 necessarily followed. f 



* C Gegenbaur denotes by primary, that part of the girdle which is preformed 



ilage; and by secondary, that which ossifies directly from membrane 

 Conybeare, op. supra cit. 



