2IO VERTEBRATE SKELETON 



bone. Premaxillae are large to accommodate the large incisors, the bone extend- 

 ing between the maxillae to the frontal. The tympanic is small and paroccipital 

 and posttympanic processes are united. There is a postglenoid process in the 

 mandibular fossa; the mandible has a moderate ramus, the coronoid process 

 being higher than the condylar which bears a broad rounded condyle. Both 

 jaws have large diastemata. 



Carnwora (Ferae) vary in shape of skull, it being either elongate (fig. 222), 

 especially in the facial part, or short and rounded. When long, a sagittal crest is 

 usually well developed, less so in short skulls, the extent of development depend- 

 ing on that of the temporal muscle. The zygomatic arch is well developed and 

 orbit and temporal fossa are connected, but the postorbital processes above and 

 below may be large (actually meeting in the mongoose). Sometimes the 

 occipital condyles extend on the basioccipital, those of the two sides meeting 

 in some Mustelids. The flat occiput is vertical or inclined backwards, parietals 

 and frontals are large, nasals and premaxillaries moderate, the latter not reach- 

 ing the frontals. The lacrimal in Fissipedia has at most a small facial part; it is 

 greatly reduced in Pinnipedia and lacking in true seals. Separate foramina 



Fig. 222. — Skull of Urocyon virginianus (Bairdj. 



opticum, ovale and rotundum occur, except in some seals where the optic nerve 

 runs through the orbital fissure. Some have an alisphenoidal canal. The hard 

 palate ends with the palatines, the choanae being at or behind the level of the 

 last molar. 



The auditory region affords features of sj^stematic use. In Aeluroidea the 

 tympanic bone is more or less annular and forms part of the tympanic wall, 

 the rest being formed by the entotympanic, so that there are two parts to the 

 tympanic cavity, separated {Hyccna excepted) by a partition. In Arctoidea the 

 tympanic bone forms the whole outer wall of the cavity (Klaauw recognizes 

 an entotympanic in the dog, figure 205) and a separate centre for the posterior 

 part in others. In Pinnipeds the tympanic bone is flat and thin (Otariidae) or 

 forms a hard, thick-walled bulla. The paroccipital process varies, sometimes 

 (Arctoids) being separate from the bulla, or may touch or even embrace it. The 

 lower jaw has a strong coronoid process, the roUer-hke condyle fits in a trans- 

 verse fossa in the squamosal and the angular process of the lower jaw is small 

 and pointed. 



Pinnipedia differ from other Carnivores in the short, round skuU with short 

 face and a constriction in the interorbital region. The alisphenoid is not always 



