POEBROTHEKIUM. 21 



The only parts preserved and visible of the base of the cranium, in the speci- 

 men, are the auditory bulljB, separated by the body of the sphenoid bone. These 

 are remarkable for their great size and position. Relatively they are not longer 

 than in the Musks, but their transverse and antero-posterior diameters are rather 

 greater. They are also more vertical in their position than in the Musks, and 

 are so situated that their postero-external portion projects considerably exterior 

 to the ramus of the lower jaw, filling up nearly a concavity formed by its posterior 

 margin. The length of the bullje from the meatus auditorius is eleven lines, the 

 transverse diameter posteriorly nine lines, and the antero-posterior diameter an 

 inch. Externally they are convex, and converge forwards within the position of 

 the ramus of the lower jaw; internally they are vertical and slightly convex, or 

 nearly plane; posteriorly they inclose the stylal pit; and postero-internally they 

 present a broad irregular surface, which abuts against the paramastoid process. 

 The space separating the bulla3, or the width of the sphenoidal body between them, 

 is about five lines. (Fig. 1.) 



The auditory process resembles that of the Musks, and the meatus auditorius 

 externus, which holds the same relative position as in these, is subcircular, and 

 about a line in diameter. 



The glenoid articulation, so far as can be ascertained by viewing its position with 

 the condyle of the lower jaw in contact, is much like that of the Musks, but 

 appears rather more concave. 



Inferior Maxilla. — The form of the lower jaw in Dorcatherium is very similar 

 to that of the recent Musks, but is very peculiar in Poehroiherium. In this the 

 base is much more nearly horizontal, and when placed upon a plane surface touches 

 it at the angle and middle, and the anterior portion, which curves downwards from 

 the position of the third premolar to the symphysis, also nearly reaches the same 

 level. (Fig. 1.) 



The outer surface of the bone below the true molars is convex, but below the 

 premolars is nearly plane and deeper than in the former position. The alveolar 

 margin rapidly ascends posteriorly from the position of the second true molar, and 

 descends in advance of the second premolar. 



The ramus is remarkable for its breadth, and the possession of an angular 

 apophysis, as in the Camel, carnivora, and most rodentia. The process in position 

 and form is intermediate to that of the Camel and Eabbit. From its point a thin 

 convex edge, corresponding to the technical angle, descends to the base of the jaw, 

 and a concavity, which in a great measure is occupied by the auditory bulla, ascends 

 to the condyle. 



The relation of the condyle and coronoid process is about the same as in the 

 Musks, but below the notch separating them, the ramus is depressed relatively as 

 much as in the Peccary, a peculiarity in which the genus differs from all existing 

 ruminants. 



The condyle externally has nearly the same form as in the Musks, and as far as 

 can be seen in the specimen; its articular surface appears to be a little more convex 

 than in those animals. 



The coronoid process is relatively broad, and curves upwards as in the Musks. 

 4 



