120 ' Prof. H. G. Seeley. The Shoulder Girdle 



leads me to doubt the substantial accuracy of the early interpretations 

 of Home, Buckland, and Cuvier, in regarding the scapula as extend- 

 ing an articular surface inward and forward towards the pre-articular 

 portion of the coracoid. Various circumstances lead me to suggest 

 that the notch on the anterior margin of the coracoid is a portion of 

 the precoracoid foramen; that the precoracoid element of the 

 shoulder girdle was cartilaginous in Ichthyosaurus ; and that this 

 cartilage usually articulated with the part of the scapula anterior to 

 the external articulation of the coracoid, and also with the anterior 

 inner processes of the coracoids, so as to complete the precoracoid 

 foramen anteriorly. Among the reasons which suggest this inter- 

 pretation are : (1) It accounts for the structure of the shoulder girdle, 

 and explains its homology ; (2) it brings the shoulder girdle of 

 Ichthyosaurus into harmony with Nothosaurus, in which there is a 

 similarly incomplete (precoracoid) foramen and similar cartilaginous 

 surfaces of coracoid and scapula in close juxtaposition ; (3) it brings 

 the shoulder girdle of Ichthyosaurus into harmony with that of the 

 Anomodontia, because they correspond in the form of the scapulae, 

 the positions and forms of the clavicles, interclavicles, and coracoids ; 

 so that, if the Anomodont precoracoid were unossified, the differences 

 from Ichthyosaurus would be small, except that some of the Anoin- 

 odonts (Pareiasaurus) develop an epiclavicle of Labyrinthodont type. 

 On this evidence a cartilaginous precoracoid is shown in the restora- 

 tion now given. 







/ 

















wor 



so 



FlG. 1. — Shoulder girdle of Ichthyosaurus, cor., coracoid ; sc, scapula ; ? pc, pre- 

 coracoid, supposed to have been cartilaginous ; cl, clavicle ; i.cl, inter- 

 clavicle. 



Before the Enaliosauria were subdivided, the bone which is here 

 named interclavicle was regarded by Sir E. Home as homologous 

 with the interclavicle of Ornithorhynchus, but it is named episternum 

 by Cuvier, Sir R. Owen, and some recent writers like K. von Zittel. 

 To the best of my belief the episternum was identified as being the 

 interclavicle by Professor Huxley. My own earliest use of the term 

 in relation to Ichthyosaurus is in 1869 (' Index to Fossil Remains, &c, 

 Woodw. Museum '). If the ossifications are membrane bones, they 

 are rightly classed as clavicles ; if they are cartilage bones, they may 

 be connected with the sternum, and take a sternal name. Each of 



