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



in each of the two branches composing the apparently single bone in 

 the mature girdle, and the apparent oneness of the bone when ossifi- 

 cation is complete is due to the coalescence of the two bony masses. 

 Further, as a result of his investigation, H. Jftathke knew that the 

 anterior ventral ray enters into the constitution of the glenoid fossa, 

 for, in his discussion of its homology, he says : " Certainly it would 

 be a very peculiar circumstance for Testudinata in connection with 

 this view (viz., that this ray is acromion) that in them the acromion 

 also takes a share in the formation of the hollow of the shoulder 

 joint."* 



This places it beyond doubt that H. Kathke found each of the two 

 rays of the " anterior bone " of the Testudinate shoulder girdle 

 entering into the composition of the glenoid fossa. 



Now, the separate ossification of each of the branches of the 

 " anterior bone," and the contribution by each to the glenoid fossa, 

 constitutes, I submit, a sufficient warrant for assigning to each equal 

 morphological value, so that if one branch (the dorsal) is scapula, 

 the claim of the other to be precoracoid (clavicular, Grotte) cannot be 

 contested. 



I repeat, between the Plesiosaurian and the Testudinate girdle 

 there is an extremely close correspondence : each is three-rayed, each 

 has a dorsal ray, each a posterior ventral ray, and each an anterior 

 ventral ray. In Testudinata, each of these three rays contributes to 

 the glenoid fossa ; and in the Plesiosaurian girdle no evidence has, 

 so far as I know, been adduced to disprove a similar composition of 

 this fossa. 



Without embryological study we had not certainly known whether 

 either, to the exclusion of the other, or both together, of the two 

 branches of the " anterior bone " in Testudinata helped to form the 

 glenoid fossa, since, when ossification is complete, synostosis is so 

 perfect that no trace of earlier separateness remains. 



Stannius, indeed, mentions a skeleton of Emys in the Berlin 

 Anatomical Museum, in which, on the left side, the anterior ventral 

 limb is suturally united with the ascending limb (scapula). This, 

 however, has been most obligingly re-examined for me by Professor 

 Dr. W. Dames, with the result that he finds the appearance of a 

 suture ambiguous and suggestive rather of an accidental crack, 

 so that this specimen has not the importance previously attached 

 to it.f 



In each of the two girdles under consideration the homology of the 

 posterior ventral ray is universally acknowledged to be identic each 

 is coracoid; and that of the anterior ventral ray cannot, I think, 



* Rathke, H., < Ueber die Entwickelung der Schildkroten/ p. 138. 

 f I am glad to take this opportunity of expressing my acknowledgment to Pro- 

 fessor W. Dames for his assistance kindly rendered me in this matter. J. W. H. 



