48 Field Columman Museum — Geology, Vol. II. 



lage bone like the precoracoid get entirely on the outside and seal in 

 a membrane or dermal bone? I would sooner believe that the 

 so-called clavicles are really precoracoids, and for this belief their 

 position on the visceral side of all three cartilage bones, the scapula, 

 episternum and coracoid, would lend some support. In no case, how- 

 ever, can I believe it probable that this cartilage represents the pre- 

 coracoid. 



The same argument will apply in its entirety to the assumption 

 that the ventral ramus of the scapula is in reality the precoracoid. 

 In no specimen has it ever been found as a distinct ossification. It 

 grows peripherally, enclosing the clavicles on their outer side. The 

 elongated clavicles unite by suture with the scapula in the Notho- 

 sauria without the intervention of any precoracoid process. By the 

 reduction of the clavicles and the extension of the acromial process in 

 these animals we would get the Plesiosaurian girdle. Is it necessary 

 to insert a distinct ossificatory element in this development? 



It may be added that Koken believes the precoracoid to be fused 

 with the coracoid. 



I cannot, therefore, believe that the precoracoid is represented 

 by any ossification in the plesiosaurian clavicular girdle. Nor do I 

 believe there is any genetic relationship between the ventral ramus 

 of the Plesiosaurs and that of the Chelonian scapula. If there is, is 

 it not strange that in the one case the branch should lie ventrad to 

 the clavicle and in the other dorsad? I am well aware that in thus 

 concurring in the views held by Seeley, Andrews, Koken, Baur and 

 others, there are pertinent arguments on the other side given by 

 Hulke, and especially Fiirbringer. * 



Pelvic Girdle. — The pubis varies but little from the usual form. 

 It is a broad, flattened plate of bone, thinned throughout, except at 

 the symphysial and acetabular articulations. It is, in general, quad- 

 rilateral in shape, with the anterior inner angle broadly rounded, and 

 the acetabular angle truncated. The posterior and outer borders are 

 both markedly concave, and of about equal length. " The anterior 

 border is more nearly straight and irregular. The inner border is 

 thickened on the posterior third or half, gradually becoming thinner 

 anteriorly. The obliquely truncated sutural surface is much rough- 

 ened. The two bones, when united, must have made an angle with 

 each other of about one hundred and twenty-five degrees. I do not 

 think that there was much cartilage between the two, or that it 

 extended back to the ischial symphysis, though it may. Anteriorly 



Jena. Zeitschr. 1900. p. 332. 



