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



me the task of re-examining the facts and the considerations on 

 which were based those statements made nine years ago, and now 

 questioned. The outcome of this enquiry I now offer to the judg- 

 ment of the Royal Society. 



In his recent paper, in addition to the known elements recognised 

 by all comparative anatomists (viz., two scapulae, two coracoids, two 

 clavicles, and an interclavicle), Professor H. G. Seeley (a) assigns 

 to the Ichthyosaurian shoulder girdle a precoracoid, cartilaginous ; 

 (b) he regards as non-proven my interpretation of the anterior of 

 the two ventral rays present in the Plesiosaurian girdle, as a pre- 

 coracoid ; (c) he considers that the process ascending from the body 

 of the scapula in Plesiosauria is not homologous with the analogous 

 vertical ray in the Testudinate shoulder girdle ; and (d) he contends 

 that certain osseous components of the Plesiosaurian girdle are 

 clavicles and interclavicle, and not omosternalia. 



It will be convenient to notice these matters serially. 



(a) The value of the evidence on which a precoracoid cartilaginous 

 has been assigned to the Ichthyosaurian shoulder girdle. 



Professor H. G. Seeley conceives the presence of a precoracoid 

 cartilaginous in this girdle which " articulated with the part of the 

 scapula anterior to the external articulation of the coracoid, and also 

 with the anterior interior processes of the coracoids, so as to complete 

 the precoracoid foramen anteriorly." 



He founds this conception mainly on the supposition that the 

 ventral end of the scapula comprises three several portions : (1) a 

 posterior portion which contributes to form the fossa glenoidalis ; 

 (2) a middle portion articulating " with the anterior, articular edge 

 of the coracoid;" and (3) an anterior which does not differ in its 

 cartilaginous, articular aspect or thickness from the middle portion, 

 but which looks inwards without any other bony element of the 

 shoulder girdle to articulate with it. 



The conception of a distinct anterior portion of the ventral end of 

 the scapula in front of that part of this end of the scapula which 

 articulates with the coracoid. therefore which is in front of the scapulo- 

 coracoid articulation, is, then, a principal reason for Professor 

 H. G. Seeley's conception of a precoracoid cartilaginous in the 

 Ichthyosaurian girdle. 



A careful study of many Ichthyosaurian scapulas disposes me to 

 regard as fallacious the appearance of a tripartite division of 

 the ventral end of the bone; such a division does not appear 

 to me to be supported by the best preserved and most perfect 

 examples. 



In a scapula, now before me, obtained by A. Leeds, Esq., from the 

 clay pits (Oxford clay) near Peterborough, which retains its normal 

 figure, texture, and surface markings, as perfectly as a newly mace- 



