CHAP, v.] THE CATS MUSCLES. 133 



rotates it from without inwards and from below upwards, and the 

 lower oblique acts in the reverse manner. 



We shall hereafter see that different nerves go to certain of these 

 muscles. The choanoid muscle is supplied by the sixth nerve. 



The levator palpclrce is another long slender muscle arising near 

 (above) the optic foramen. It is inserted into the upper eyelid, 

 which it raises. No analogous muscle depresses the lower eyelid. 



The buccinator is a thin, delicate muscle extending between the 

 alveolar margins of the jaws on each side of the mouth (Fig. 77, B). 

 Its fibres cross each other near the middle of the muscle, and it is 

 perforated by the duct of the parotid gland. It adjoins internally the 

 mucous lining of the mouth ; externally, it is partly covered by the 

 muscle next described. 



The masseter (M) is a short and very thick muscle (in two layers) 

 which arises from the malar and under surface of the front part of 

 the zygoma. Its fibres pass thence obliquely backwards (those of 

 the outer layer, very obliquely), to be inserted into the concave outer 

 surface of the ascending ramus of the mandible. Externally, this 

 muscle is only covered by skin and fascia. Its action is to raise the 

 lower jaw, and is therefore an important agent in mastication. 



Each temporally (T) covers the side of the skull, almost meeting its 

 fellow of the opposite side at the sinciput. Each arises in two layers, 

 from the side of the skull (from the lambdoidal ridge to the postorbital 

 process of the frontal) and being thick and fleshy, fills up the tem- 

 poral fossa (to which it gives its name) within the zygoma. Its fibres 

 converge (fan-wise) to its insertion into the coronoid process of the 

 mandible. Its action raises the lower jaw, and thus enables the animal 

 to take a very firm grip of any struggling prey it may have seized. 



The pteryyoidcm intcrnus is a strong muscle which arises from the 

 pterygoid fossa. Its fibres descend obliquely forward to its insertion 

 in the inside of the angular part of the mandible. It is close to the 

 masseter inferiorly, being only separated from the latter beneath the 

 margin of the mandible, by aponeurosis. It acts with the masseter 

 in raising the lower jaw. 



The pteryyoideus extcrnm arises from the outside of the pterygoid 

 and pterygoid plate of the sphenoid, and is inserted into the inside of 

 the neck of the mandibular condyle, and thence forwards to the 

 orifice of the dental foramen. In its action it is also an elevator of 

 the mandible, since though by its direction it tends to draw the 

 mandible somewhat backwards, it cannot do so owing to the opposi- 

 tion of the post-glenoid process. 



The digastric is a large muscle which arises from the skull behind the 

 external auditory meatus, i.e., from the paroccipital. It is inserted into 

 the inside of the anterior half of the inferior margin of the mandible. 



The middle portion of the muscle is very aponeurotic internally, 

 externally, and below. Its action is to depress the lower jaw and 

 open the mouth (D). 



The stylo-hyoid (sty-h) is a longish muscle which descends from the 

 mastoid process to the side of the hyoglossus. 



