SKELETON OF CARNIVORA. 



499 



canine tusk. The premaxillaries, 22, are minute. There is a 

 large oval vacuity in the lateral wall of tlie posterior nares. The 

 skull is singularly expanded, short, obtuse, and, as it were, trun- 

 cated anteriorly ; and, being constricted between the orbits, the 

 upper surface presents an hour-glass form. The parietes of the 

 cranium are thick and dense, witli a diploc, gradually degene- 

 rating into a coarse cellular texture, in the enormous mastoids. 

 The tentorium is bony, the sella turcica large and shallow, with 

 anterior and posterior clinoid processes, and the crista galli is 

 jn-ominent. The petrosal terminates below in three obtuse pro- 

 cesses, but there is no bulla ossea. The pterygoid process is per- 

 forated by the ectocarotid. The bony roof of tlie palate is very 

 concave towards the mouth, and terminates behind by a broad 

 biangular notch. The tympanic cavities are smooth, and almost 

 hemispheric : the antorbital canal is large : the nasal fossai con- 

 tract as they pass forward to the vertical external nostril. The 

 osseous part of the septum narium is formed by the canaliculate 

 vomer and the coalesced plates of the prefrontals, dividing the 

 posterior halves of the olfactory chamber. The lateral sinuses 

 are completely surrounded by bone. A vein perforates the back 

 part of the parietals and terminates in the longitudinal sinus. 

 The bony tentorium terminates above the base of the petrosal ; a 

 thick, smooth ridge enters the lower half of the fissure between 

 the anterior and posterior cerebral lobes. A similar but shorter 

 ridge from the inner side of the frontal more completely defines 

 the rhinencephalic chamber : an elliptic foramen leads from the 

 lower and outer corner of this fossa into the back part of the 

 orbit between the orbitosphenoids and 

 frontals. The mandible, S2, articulates 

 by a thicker condyle than in true 

 Seals : it is terminal : the feeble angle 

 slopes forward from it : the coronoid 

 is oblique and rounded. 



In the Bear-tribe, as in the Seals, 

 the tentorium is ossified : the inter- 

 parietal unites with and forms a trian- 

 gular process of the superocci})ital : 

 the alisphenoid articulates with the 

 parietal : the ectocarotid pierces the 

 l^terygoid process. There is no ptery- 

 goid fossa. 



In the European Black and Brown Bears ( U?\sits arcfos) the 



339 



of Walrus {Trirhccus nKimayiis). 



frontal region of the skull is 



•aised and convex. 

 K K 2 



In the A 



merican 



