296 ACTIVE ORGANS OF MASTICATION. 



it consists of two layers separated by some fat, vessels, and 

 nerves. Turn this fascia down to the zygoma, and the up- 

 per and larger portion of the temporal muscle is exposed. 

 Now saw through the zygomatic arch at either end, and 

 turn it down with the masseter, and we have brought to 

 view the lower portion of the temporal. Thus exposed, the 

 temporal muscle is seen to arise on the side of the cranium 

 from the whole length of the semicircular ridge, and from 

 the surface below this ridge, formed by the frontal, parie- 

 tal, squamous portion of the temporal, and greater wing 

 of the sphenoid bone, as low down as its crest ; and from 

 the under surface of the fascia temporalis. From this ex- 

 tensive origin, the fibres converge to a strong tendon, 

 which is inserted into the coronoid process, nearly sur- 

 rounding it, and continues forwards as far as the last 

 molares. 



Function. To bring the lower jaw to the upper, in the 

 cutting of the food in mastication. The posterior fibres, by 

 drawing the lower jaw backwards, are a great security 

 against dislocations of this bone. 

 3. Pterygoideus externus. 



Dissection. Turn off the masseter muscle close to the 

 bone, and take out a section of the ramus by sawing be- 

 FlG - 84 - tween its angle,, and the root of 



the condyle, and the pterygoid 

 muscles will be exposed. 



The pterygoideus externus is a 

 short triangular muscle, running 

 horizontally and situated deep be- 

 hind the ramus of the lower jaw. 

 It arises by two heads the one 

 from the crest on the great wing 

 of the sphenoid bone, at its root, the other from the outer 

 surface of the external pterygoid plate, and tuberosity of 

 the upper maxilla the two portions converge and pass 



FIG. 84 represents the Pterygoid Muscles; the zygomatic arch and ramus of 

 the lower jaw being removed, a 6 Pterygoideus externus. c Pterygoideus 

 interims. 



