THE HEAD AND NECK. 87 



these conditions, this being the line of least resistance. Such cases of regurgita- 

 tion are met as sequels of diphtheria. 



9. Locate the tonsil. 



It is between the anterior and posterior pillars of the fauces ; it corresponds 

 in position to the angle of the jaw ; the superior constrictor of the pharynx is 

 external to it, while the internal carotid artery is fully one inch from it. It is 

 the ascending pharyngeal artery, between the tonsil and the superior constrictor, 

 and not the internal carotid artery that is in danger of being wounded in tonsil- 

 lotomy. 



i o. Explain the mylo-hyoid nerve. 



It is a branch of the inferior dental, being given off while this nerve is 

 between the ramus and spheno-mandibular ligament. It pierces the spheno- 

 mandibular ligament, passes along the mylo-hyoid groove, and supplies the 

 anterior belly of the digastric and the mylo-hyoid muscle. This nerve is a part 

 of the motor root of the fifth, ensconsed in the sheath of the (sensory) inferior 

 dental part of the fifth, given off from the Gasserian ganglion. (Fig. 53.) 



1 1 . Name and explain fully the structures attacked to the styloid process of the 

 temporal bone. (Fig. 44.) 



There are three muscles and two ligaments: (i) The stylo-hyoid muscle. 

 This muscle arises from the back and outer surface of the styloid process, near the 

 base. It lies above the posterior belly of the digastric muscle. Near its inser- 

 tion into the body of the hyoid, at the junction of the body and greater horn, 

 it bridges the intermediary tendon of the digastric. In its action it is synergistic 

 with the posterior belly of the digastric, the two being supplied with motion by 

 the seventh nerve. (2) The stylo-glossus muscle arises from the front and tip of 

 the styloid process, also from the upper part of the stylo-mandibular ligament. 

 It is inserted into the side and under surface of the tongue. Its action is to draw 

 the sides of the tongue up to make the dorsum of this organ concave from side 

 to side. (3) The stylo-pharyngeus arises from the base of the styloid process, 

 opposite the stylo-hyoid. It is inserted, with the palato-pharyngeus, into the thy- 

 roid cartilage, and also into and with the constrictors of the pharynx. (4) The 

 stylo-maxillary or stylo-mandibular ligament will be seen in your dissection as a 

 process of deep cervical fascia, a derivative of the third layer, between the 

 masseter and internal pterygoid muscles. It separates the parotid from the 

 submaxillary gland. It gives origin to one head of the stylo-glossus muscle. 

 (5) The stylo-hyoid ligament extends, as a small elastic fibrous cord, from the 

 tip of the styloid process of the temporal bone to the lesser cornu of the hyoid 

 bone. It frequently becomes ossified. Occasionally it is of enormous size. 



12. Describe tJie external pterygoid muscle. (Fig. 49.) 



This muscle has two origins and two insertions. The upper head arises from 

 the under surface of the greater wing of the sphenoid bone, limited internally by 

 the foramen ovale, transmitting the third division of the fifth nerve, and the fora- 

 men spinosum, transmitting the great meningeal artery ; externally, the origin of 

 this head is limited by the pterygoid ridge. The lower head arises from the 

 greater part of the outer surface of the external pterygoid plate. The upper 

 head is inserted into the interarticular fibro-cartilage ; the lower into the front of 

 the condyle. The action of the muscle is to draw the condyle well forward, 

 and with it also the interarticular cartilage. It also moves the jaw to the oppo- 

 site side, and assists to some extent in opening the mouth. 



13. Describe tlic internal pterygoid muscle. (Fig. 49.) 



It arises from the inner surface of the external pterygoid plate, and from the 

 tuberosity of the palate bone. It is inserted into the inner surface of the ramus 

 of the mandible, limited above by the mylo-hyoid ridge and inferior dental foramen. 

 The action is to close the mouth and draw the jaw forward and to the mid-line. 



