232 Mammalia. 



gold raise the lower jaw against tlie upper ; and tlie two latter 

 muscles, from tlie obliquity in the direction of their fibres, 

 assist the External Pterygoid (to be seen later, after the 

 removal of the Zygomatic arch) in drawing the lower jaw for- 

 wards upon the upper ; the jaw being drawn back again by 

 the deep fibres of the Masseter and the posterior fibres of the 

 Temporal. 



Second Group. The Digastric depresses the lower jaw. 



Third Group. The Stylo-hyoid, Mylo-hyoid, and Genio- 

 hyoid together raise the Hyoid hone, and with it the base of 

 the tongue, during the act of deglutition. 



Fourth Group. The Genio-hyo-glossi, Hyo-glossi, and 

 Linguales act separately. The Genio-hyo-glossi, by means 

 of their posterior and inferior fibres draw upwards the Hyoid 

 bone, bringing it and the base of the tongue forwards, so as 

 to protrude the apex from the mouth : their anterior fibres will 

 restore it to its original position by retracting the organ 

 within the mouth. The whole length of this pair of muscles 

 acting along the middle line of the tongue will draw it down- 

 wards, so as to make it concave from before backwards, and 

 form a channel along which fluids may pass to the Pharynx. 

 The Hyo-glossi draw down the sides of the tongue, so as to 

 render it convex from side to side. The Linguales by drawing 

 downwards the centre apex of the tongue render it convex 

 from before backwards.* 



Examination of Internal Pterygoid, and Stiperior 

 Constrictor Muscles. The Student will now take a fine 

 saw, and cut through the zygomatic arch in two points ; an- 

 teriorly, just behind the orbital ring ; and posteriorly, about 

 an inch from the same : he will then raise that part of the 

 ramus of the jaw which still remains, and will first cut across 

 a small muscle in the neighbourhood of the molar teeth, 



Gray. 



