1222 A MANUAL OF ANATOMY 



Insertion.— {i) The superior and posterior borders of the ala of 

 the thyroid cartilage, and (2) the lateral Wall of the pharynx, its 

 fibres blending with those of the palato-pharyngeus and middle 

 constrictor muscles. 



Nerve-supply. — ^The glosso-phar3mgeal nerve. 



The muscle is directed downwards and inwards. 



Action. — To elevate the pharynx and larynx. 



The muscle passes between the superior and middle constrictor 

 muscles. The glosso -pharyngeal nerve lies at first along its lower 

 border, and then crosses over it on its way to the posterior part of 

 the tongue. 



Internal Carotid Artery. — ^The internal carotid artery is one of 

 the terminal branches of the common carotid. It commences on 

 a level with the upper border of the thyroid cartilage, and passes 

 vertically upwards to the under surface of the petrous part of the 

 temporal bone. Here it enters the carotid canal within the pars 

 petrosa, and, after traversing this canal, it enters the cranial cavity. 

 The vessel is divided into three parts — extracranial or cervical, 

 petrous, and intracranial or cavernous. 



Extracranial or Cervical Part. — ^This part of the vessel extends 

 from the level of the upper border of the thyroid cartilage to the 

 foramen caroticum on the inferior surface of the petrous part of 

 the temporal bone. Its coruse is vertically upwards, and at first 

 it lies in the carotid triangle, where it is placed external to, and 

 behind, the external carotid artery. 



Relations — Anterior. — ^This part of the vessel is comparatively 

 superficial, being covered by the integument, platysma myoides, 

 and stemo-cleido-mastoid, the latter overlapping it. After leaving 

 the carotid triangle the artery becomes deeply placed, and passes 

 beneath the posterior belly of the digastric and stylo-hyoid muscles, 

 parotid gland, styloid process, and stylo -pharyngeus muscle. In 

 this part of its course the vessel is crossed by the hypoglossal, 

 glosso-pharyngeal, and pharyngeal branch of the pneumogastric, 

 nerves, and by the occipital and posterior auricular arteries. The 

 relation of the artery to the external carotid here undergoes a 

 change. The level where the change takes place is as the internal 

 carotid passes beneath the styloid process of the temporal bone, 

 and the change consists in the external carotid taking up a position 

 directly anterior to the internal carotid. The two arteries are, 

 however, separated from each other by the following structures : 

 (i) the styloid process ; (2) the stylo-pharyngeus muscle ; (3) the 

 glosso-pharyngeal nerve ; and (4) the pharyngeal branch of the 

 pneumogastric nerve. 



Posterior. — ^The rectus capitis anticus major, the superior cervical 

 ganglion of the sympathetic, and the superior laryngeal branch of 

 the pneumogastric nerve. 



External. — ^The internal jugular vein and pneumogastric nerve, 

 the nerve being on a plane posterior to both artery and vein. These 

 three structures are still surrounded by a sheath which is an upward 

 extension of the carotid sheath, previously described. Close to the 



