MORPHOLOGICAL REVISION 



89 



The centrum of the eighteenth is of much smaller diameter but of greater 

 length than the anterior vertebrae, and has very prominent neural and 

 hsemal spines. These are high and narrow with expanded extremities and 

 give the vertebra a flattened appearance vertically. The distal ends of the 

 neural and haemal spines are heavy, with flat rugose faces, which have the 

 appearance of having been attached to heavy plates of cartilage or perhaps 

 bone. On the last vertebrae observed the distal ends of the hsemal spines 

 are so elongate that they touch the spines of the adjacent vertebrse. 



The ribs are relatively heavy and short, with little curvature and widely 

 separate capitulum and tuberculum. 



The clavicles and interclavicle (plate 12, fig. 3) unite to form a thin, 

 heart-shaped plate, covered on the outer surface with a sculpture similar to 

 that of the skull. The clavicles overlap the anterior end of the interclav- 

 icle below. From the outer edge of the clavicle a smooth, conical process 

 extends upwards and inwards, possibly for the attachment of the scapula. 

 The interclavicle is rhomboidal, with no posterior prolongation; the posterior 

 edge is marked as if by the squamous attachment of some element, unknown 

 as yet. 



Fig. 23. — D. magnicornis. After Williston. No. 652 Univ. of Chicago. X K- 



A. Dorsal view of right humerus. D. Posterior view of femur. 



B. Lower view of same. E. External view of same. 



C. Cross-section of proximal end of same. 



The coracoid: Williston has discovered a small oval plate lying on the 

 upper side of the clavicle in specimen No. 652 University of Chicago, and 

 less perfect remains of this bone are found in specimens No. 4539 and 4748 

 Am. Mus. It is thin, nearly oval in shape, with a slight thickening of the 

 posterior part to receive the humerus. A small foramen pierces the inner 

 side, back of the middle and not far from the edge. 



The scapula is unknown. 



Previous to 1909, none of the numerous skeletons of Diplocaulus col- 

 lected had any trace of associated limb bones, and the animals were regarded 

 as limbless. Dr. Williston reports (70) finding limb bones with several 

 specimens, in what he regards as unquestionable association. Specimens 

 Nos. 650, 651, and 652 University of Chicago show these bones. 



The humerus is rather short, without well-formed articular surfaces. 

 The two extremities are expanded and turned at an angle of 45° to each 

 other. The distal end is larger and more thickened than the proximal and 



