MORPHOLOGICAL REVISION 



99 



The single sacral rib is large, with a single head, divided into distinct 

 facets, which lie at an angle to each other and fit the facets on the pleuro- 

 centrum and transverse process, and the intercentrum. A slight constric- 

 tion forms a neck which separates the head from the body of the rib. The 

 body is flattened and curved to the rear; the outer surface fits accurately 

 into a depression, which runs obliquely across the inner face of the ilium 

 from above backwards and downwards. There is no rugosity on either bone 

 at the points of contact, but the two fit very closely. This relation of the 

 sacral rib to the ilium is of great importance, as on it depends the position 

 of the whole pelvis. The relationship is confirmed by its occurrence in three 

 specimens. 



The caudal ribs are free as far back as the fifth vertebra, but ribs are 

 absent beyond this. 



The shoulder girdle and fore limbs (No. 4186 Am. Mus.) : This is the speci- 

 men figured by Cope. The anterior portion of the clavicle is broad and some- 



FiG. 30. — Eryops megacephalus . 



A. Inner view of left sacral rib and ilium, showing relation of bones. No. 4292 Am. Mus. X H- 



B. Inner view of left sacral rib. No. 4307 Am. Mus. X }4. 



C. Outer view of same. 



what convex outward; the bones of the two sides overlap in the specimen, 

 and probably did so to some considerable extent in the living animal. The 

 posterior third is bent almost at right angles to the anterior part, and lies 

 on the upper edge of the scapula, overlapping it somewhat on the inner side; 

 this part of the clavicle lies beneath the anterior end of the cleithrum. The 

 edges of the clavicle are thin, and the anterior and posterior edges show a 

 tendency to fray out into thin projections, but a strengthening ridge runs 

 its full length, about one-third of the way from the top. The outer surfaces 

 of both the clavicle and interclavicle are smooth and without radiating 

 ridges. 



The interclavicle is rhomboid in form without posterior prolongation; 

 the anterior edge carries a few blunt, flattened spines. 



The scapula shows no evidence of separate procoracoid or coracoid bones; 

 these were apparently cartilaginous. The anterior end is slightly convex 

 in most specimens. The posterior end is but little widened and the upper 



