92 



THE OSTEOLOGY AND MYOLOGY 



the teeth" almost invariably takes place when the animal is irritated ; but the muscles upon 

 the face itself have but little eflect in "its production, compared with the action of the 

 panniculus. I cannot find any muscles upon the lower jaw distinct from the orbicularis 

 and buccinator, to correspond to the several described in anthropotomy ; nor do I think 

 that any such exist. There are, however, two very distinct muscles upon the side of the 

 face, subserving the movements of the snout and anterior part of the upper lip, which I 

 shall describe under the names of zygomaticus and levator labii superioris, without feeling 

 at all sure that these names indicate their homology. It is worthy of note, that while these 

 "muscles of expression" of the human subject mainly draw the mouth in different direc- 

 tions, in the present case they move the snout, and only secondarily affect the lips. 



Zygomaticus. — This is the principal fucial muscle ; of large size, definite origin and 

 insertions, \and of deeper color than the rest, probably in consequence of its constant 

 action. It lies nearly parallel with the alveolar border of the upper jaw, but still has 

 some downward inclination as it passes forward. It arises fleshy from the root of the 

 zygoma, in the slight depression of the malar bone just below the infraorbital ridge, filling 

 this depression to the general level. It forms a flattened mass that may be divided almost 

 to its origin into distinct fasciculi. These fasciculi are from three to six in number ; cor- 

 responding to as niiuiy slender, terete, but strong, tendons. These tendons are as distinct 

 as, and call to mind, those of a digital flexor. They run forward, embedded in the sub- 

 cutaneous cellular tissue, as well as in the muscle about to be described, and penetrate to 

 the skin itself They are directly inserted into the skin of the nostrils at various places 

 about the side of the snout. Neither the number nor the insertion of these tendons is con- 

 stant ; frequently only one or two reach the extremity of the muzzle, the rest being 

 inserted into the skin of the lip just back of the nostrils. It is diflicult to describe with 

 exactness the action of this muscle ; its several disconnected tendons effect the varied and 

 delicate movements of the extremity of the snout, and of the nostrils themselves, that 

 may be observed when the animal is sniffing about after food. 



Levator lahii superioris. — The action of the foregoing is aided and extended to the 

 greater part of the upper lip, by means of the present muscle. It arises from the side of 

 the superior maxillary, just below the preceding, a little above the alveolar border, at or 

 near the articulation of the malar, and passes forward and downward, to be inserted into 

 the side of the lip and muzzle. It is entirely fleshy. It draws the lip upward and back- 

 ward, and the nostril directly backward. Its insertion, not precise at best, varies with 

 individuals ; and its bony origin is likewise variable. 



Muscles of the Under Jaw. — The enormous bulk of the muscles that close the jaws 

 indicates the force with which this action may be performed. These muscles fill the deep 

 temporal fossa, from the orbit to the occiput, and from the sagittal crest to the zygoma, 

 rendering the cranial depression convex in all directions ; and also form a bulging mass 

 both on the inside and outside of the ramus of the jaw. The latter masses are prom- 

 inently displayed, without dissection, by simply opening the animal's mouth. The external 

 pterygoid, or rotatory muscle, on the other hand, is very small and feeble, correspondently 

 to the character of the maxillary articulation, that admits of but slight lateral movement 

 of the jaws. 



Masseter. — This muscle not only forms a bulging mass upon the jaw-bone, from the 

 zygoma to the border of the mandible, but fills the space between the coronoid process 



