214 



THE STUDY OF ANIMAL LIFE CHAP. 



FIG. 58. THE SKULL OF A LION. 



CA, the canine teeth, strong and sharp for killing; in front of them 

 (hidden on the lower jaw in the drawing) are the small incisors which are 

 not of much importance. In this respect a carnivore may be contrasted 

 with a grazing animal like a horse, where the incisors are Very important 

 for cutting the grass, and the canines are unimportant. The back teeth 

 of the horse have flat upper surfaces suited for crushing and grinding the 

 food ; those of the cat-tribe and dog-tribe among carnivores are adapted 

 for cutting, like compressed blades. There is a specially strong and sharp 

 back tooth (S), the sectorial or carnassial, which is in this case the third 

 premolar above and the single molar below. 



The lower jaw or mandible (MN) works in a deep glenoid fossa (G), 

 and has only an up-and-down movement. It is prevented from slipping 

 backwards by a curved post-glenoid process. This kind of articulation 

 should be contrasted with that in a sheep or in a rabbit. To the mandible 

 and in great part to its ascending process (A) powerful muscles are attached, 

 which fill up the large temporal fossa between the squamosal (SQ) and its 

 zygomatic process (Z). The semicircular zygomatic arch, made of the 

 jugal (J) in front and the forward extension (Z) of the squamosal behind, 

 protrudes greatly, and this is associated with the great mass of the jaw 

 muscles which lie within it. It should be contrasted with the non-pro- 

 truding zygomatic arch of the horse, where, moreover, a bridge of bone 

 runs from the jugal (J) to the frontal (FR), bounding the orbit (O) behind. 

 In carnivores " the orbit is confluent with the temporal fossa." 



At the back of the skull a strong crest or ridge (OR), the occipital crest, 

 extends transversely and serves for the insertion of muscles from the neck 

 and the jaw. This may be thought of in connection with the carnivore's 

 habit of dragging its prey along the ground or lifting its young one in its 

 mouth. The crest gives the muscles stronger grip. At right angles to 

 the occipital crest runs the sagittal crest (CR) along the mid-dorsal line. 

 It seryes for the insertion of muscles from the jaw. 



CO is one of the occipital condyles, formed by the ex-occipital bones. By 

 means of the condyles the skull works in two cavities in the first vertebra 

 the atlas. In front of the condyle there is in cat-like and dog-like (not in 

 beai'-like) carnivores, a strong tympanic bulla (TB) protecting the drum 

 of the ear. Vindicates the ear-hole, PA, the parietal ; FR, the frontal ; 

 N, the nasal ; PMX, the premaxilla ; MX, the maxilla. 



