THE MUSCLES OF THE NECK AND BACK 175 



4. M. pterygoideus intcrnus arises also by two heads one 

 from the pterygoid fossa, the greater portion from the inner 

 surface of the external plate, from the tuberosity of the palate 

 bone between the two plates; a second small slip outside of 

 the external pterygoid muscle from the tuberosities of the 

 palate and superior maxilla; the fibers pass downward, back- 

 ward, and outward to be inserted into the inner surface of 

 the ramus of the mandible, between its angle and dental fora- 

 men; it is disposed in a way corresponding to the insertion 

 of the masseter on the outer surface of the mandible near 

 the angle. 



Nerves. All from the inferior maxillary division of the 

 fifth cranial. 



Actions. Masseter, temporal, and internal pterygoid elevate 

 the lower jaw; the external pterygoid protrudes the lower 

 jaw, or alternately produces a grinding of the molar teeth; 

 it may also assist in opening the mouth when the condyles 

 are carried forward upon the articular eminences. The back 

 part of the temporal and the deep part of the masseter retract 

 the jaw. 



THE MUSCLES AND FASCLffi OF THE TRUNK 



THE MUSCLES OF THE NECK AND BACK 



The fascia covering the first layer of muscles is divided into 

 a superficial and deep layer. 



The superficial fascia is found beneath the skin. Contains 

 considerable adipose tissue and is continuous with the super- 

 ficial fascia covering the rest of the body. 



The deep fascia is a thick fibrous layer, which covers over 

 and forms sheaths for the muscles. It is attached to the oc- 

 cipital bone, the crest of the ilium, the spines of the vertebra?, 

 and the spine of the scapula. In the neck it forms the posterior 

 portion of the deep cervical fascia; in the thorax it blends 

 with the axillary fascia and deep fascia of the thorax; it is 

 continuous with abdominal fascia surrounding the muscles; 

 forms the dorsal layer of the lumbar fascia, and covers the 

 erector spinse mass of muscles. In the back of the thorax it 

 is called the vertebral aponeurosis. 



