DAKOTA AND NEBRASKA. 75 



mastoid process. Between the wing-like processes at the summit of the inion, the 

 surface forms a deep concavity, divided at the middle by a narrow vertical ridge. 



The occipital foramen and condyles form the termination of a more prominent 

 portion of the inion than in the Peccary. The occipital foramen is transversely oval, 

 but differs little in its diameters The condyles resemble those of the Peccary, 

 but approach less near together below. 



The paramastoid processes are strong, and apparently of variable length in the 

 different species. 



The basi-occipital is of moderate breadth, and is produced inferiorly into a median 

 crest, which expands in front to conjoin a similar enlargement of the basi-sphenoid. 

 The under surface of the latter and that of the presphenoid form a continuous and 

 moderate slope forwards into the nose. 



The external pterygoid plates are directed obliquely downward and forward, and 

 have an obtuse posterior margin. The internal pterygoid plates descend vertically, 

 and end in a process projecting a little below the position of the external plates. A 

 narrow angular groove or pterj-goid fossa occupies the interval of the external and 

 internal plates postero-inferiorl}'. 



The pterygoid plates, conjoined in the usual manner with the prolongation back- 

 ward of the palate bones, enclose between them and the latter a large median 

 palatine notch, which extends nearly as far forward as the position of the last molar 

 teeth. The sides of the notch as formed by the palatines are thick and rounded, and 

 are impressed with muscular attachments. 



Lateral palatine notches extend between the prolongations of the palate bones and 

 the obtuse ends of the alveolar borders, with their bottom a little in advance of the 

 middle palatine notch. 



The glenoid articulation exhibits a broad surface extending outwardly on the 

 under part of the posterior root of the zygoma. Its fore part is nearly straight and 

 horizontal transversely, and is moderately convex antero-posteriorly, inclining 

 forward internally and backward externally. Postero-internally it descends upon a 

 remarkably large and strong post-glenoid tubercle, which is antero-posteriorly com- 

 pressed mammillary in shape. 



The tympanies form a bulla or auditory capsule, varying in extent of development 

 in a remarkable degree in the different species of Oreodon. The bulla abuts behind 

 against the paramastoid process, externally partially encloses a space accommodating 

 the styloid process, and anteriorly extends between the basi-occipital, sphenoid and 

 squamosal in the ordinary manner among ruminants. The auditory process or 

 inferior boundary of the external auditory meatus is of moderate length, and extends 

 outward, upward and backward in a high, narrow archway between the post-glenoid 

 and post-auditory processes. 



