478 E. G. Case — Dimetrodon incisivus. 



motion of the humerus was closely restricted to a plane parallel 

 with the ground. 



The pelvis is complete and mounted nearly free, being 

 attached only by the outer side of the right half : this leaves 

 the whole sacral series of vertebrae open to inspection. The 

 posterior limb is placed with the femur pointing slightly 

 upward and forward ; this is rather the conventional than the 

 usual resting attitude of the creeping reptiles, but is not an 

 impossible or even an unusual attitude. 



The carpus and tarsus are modeled in plaster ; the first 

 after the well-preserved carpus discovered by the author some 

 years ago and now in the possession of the University of 

 Chicago, and the tarsus, except for the astragalus, calcaneum 

 and centrale 2, after the primitive type of the reptilian carpus. 

 Elements of both carpus and tarsus are not lacking in the col- 

 lection but were not included in the mount because of the 

 impossibility of assembling sufficient bones of the correct size. 



The ribs are all restored in plaster after well-authenticated 

 specimens. 



The tail has been made i*elatively short in consonance with 

 the ideas of the author, but as no specimen has yet been dis- 

 covered in which the tail is complete the exact number of ver- 

 tebrae is uncertain. 



The completion of this mount is the first attempt to assem- 

 ble all parts of the skeleton of Dimetrodon in a natural posture. 

 Its accomplishment is largely due to the patience and skill of 

 Dr. E. L. Troxell, who, as preparator, cooperated with the 

 author in assembling and placing the bones. 



