124 A MANUAL OF ANATOMY. 



Pterygoideus Internus. Fig. 1 2. 



Origin. From the pterygoid fossa, tuberosities of the 

 superior maxillary, and palate bones. 



Insertion. Into the inner surface of the ramus and 

 angle of the lower jaw below the inferior dental foramen. 



Nerve Supply. The inferior maxillary. 



Action. To close the jaw, to draw it forward, to assist 

 in the grinding movements. 



DISSECTION. 



Clean the constrictor muscles, and remove the prevertebral fascia from 

 the muscles it covers. 



The Pharynx. 



This is a fibromuscular cavity situated at the base of 

 the skull, behind the nasal (above) and buccal (below) 

 cavities and larynx, and in front of the spinal column. 



Its length is four and one-half inches from the base of 

 the skull to the level of the cricoid cartilage opposite the 

 fifth cervical vertebra. Its cavity is flattened from before 

 backward, and at its lower portion becomes obliterated by 

 the contact of its anterior and posterior walls (except dur- 

 ing swallowing). 



Into it open the posterior nares (2), the Eustachian tubes 

 (2), the mouth (i), the larynx (i), and the oesophagus (i), 

 (total 7). The soft palate projects into it from the front 

 and divides its cavity into the nasal (above) and the buccal 

 (below) portions. 



Its walls are composed of mucous membrane, fibrous 

 tissue (pharyngeal aponeurosis), and muscles (the three 

 constrictors, stylopharyngeus, and palatopharyngeus.) 



The pharynx is attached above, to the base of the skull 

 (base of sphenoid, petrous portion of temporal and Eus- 

 tachian tube, and internal pterygoid plate) ; in front, to the 



