1 16 Bulletin Ante) ican Museum of Natural History. [Vol. X, 



auditory meatus. Immediately behind the point of junction of 

 these two parts is seen the deep recess where the hyoid arch is 

 articulated to the skull. In Pocbrotherium the inner portion of 

 the bulla is much the larger, and the recess for the tympanohyal 

 is inconsiderable. In Gojuphothcriuni the two parts are about 

 equal in size, and the tympanohyal recess much more pro- 

 nounced. In the living genera, Camelus and Auchenia, the inner 



Fig. 12. Humerus, ulna and radians of Goiiiphotheriuin siir>ibergi. 



part of the bulla is much reduced and the tympanohyal recess 

 is converted into a deep circular pit surrounded by bone. 



In the skeleton of the limbs the lower end of the femur is 

 peculiar in the unusual size and development of the areas of 

 attachment of the outer and inner heads of the gastrocnemius. 

 This same peculiarity is seen in the femora of old individuals of 

 both Poebrothcrium lahiatuui and Procaiiielus occide/italis, altliough 

 to a somewhat less extent, and is doubtless a result of age. The 

 liead of the humerus shows the first distinctive change leading to 

 the development of the double l)ici])ital groove, a feature so char- 



