6O ANATOMY AND PHYSIOLOGY FOR NURSES 



v Pterygomaxillary Region. In this region there are 

 two muscles on each side the internal and the external. 

 They are very powerful in their action. 



The internal pterygoid is a thick, quadrilateral muscle, 

 resembling the masse ter in form and structure, and the 

 fibers run in about the same direction. 



, The external pterygoid is a short, thick muscle, broader 

 at its base, and arises by two heads from the sphenoid 

 bone by one head, and from the pterygoid plate of the 

 ethmoid, palate, and maxillary bones by the other. 

 Insertion, to the lower jaw. Action, raises the lower jaw 

 with great force, drawing the lower jaw forward upon the 

 upper jaw, while the masseter draws it backward, assisted 

 by the temporal ; by alternation of the muscles of each side 

 the food is comminuted and prepared for swallowing. 



MUSCLES OF THE NECK 



The muscles of the neck are : Platysma myoides, sterno 

 cleidomastoid, sternohyoid, sternothyroid, thyrohyoid, 

 omohyoid, digastric, stylohyoid, geniohyoid, geniohyoglos- 

 sus, hyoglossus, styloglossus, and lingualis. 



Platysma Myoides. Arises from the deep fascia over 

 the pectoral, deltoid, and trapezius muscles. Insertion, 

 in the lower jaw at the angle of the mouth, and blends with 

 the muscles of the face. Action, depresses the jaw and 

 angle of the mouth, also wrinkles the skin of the neck; 

 its nerve-supply is obtained from the facial nerve, through 

 the inframaxillary branches. 



Sternocleidomastoid. Arises from the upper part 

 of the sternum and inner border of the clavicle. Inserted 

 in the mastoid process of the temporal bone and two- 

 thirds of curved line of the occipital bone. Action, flexes 

 the head on the neck and chest and rotates the chin to 

 the opposite side. Nerve-supply, from the spinal acces- 

 sory, second and third cervical, anterior branches. When 



