476 



E. C. Case — Dimetrodon incisivus. 



spines were in the most relaxed position, and they have been 

 mounted in the most regular position and arrangement per- 

 mitted by the condition of the spines and the vertebrae to 

 which they are attached. There can be little doubt that the 

 position of the spines varied in each individual and were not 

 infrequently distorted by injuries, so the position given in the 

 mount is probably as correct as may be. 



Notable is the sudden increase in height of the spines in the 

 cervical region and the almost equally sudden decrease in 

 height in the sacral and anterior caudal region. 



Fig. 4. 



Fig. 3. 



Fig. 3. Photograph of the skull of 

 Dimetrodon gigas Cope. x "21. 



Pig. 4. Photograph of the 



fore limb and shoulder girdle. 



xl6. 



The shoulder girdle is mounted nearly complete ; the inter- 

 clavicle, the clavicles, the scapula of the left side complete, and 

 the lower part of the scapula of the left side all being in plain 

 view and as free as their support permits. Though a slight 

 distortion of the bones makes the exact outline of the shoulder- 

 girdle somewhat uncertain, the author believes that the depar- 

 ture from the normal curvature is very slight. No cleithrum 

 has been placed in the mounted skeleton as no bones which 

 could be referred to this element was found in the abundant 

 material. 



The humerus is placed in an almost exactly horizontal posi- 

 tion, extending directly outward from the cotylus. It is evi- 

 dent from the position of the scapula and its cotylus that the 



