The Head and Xeck. 245 



(d) The twelfth (hypoglossal) nerve arises behind the foregoing 

 nerves, since it comes from the hypoglossal foramina of the 

 occipital. It crosses their roots, forming a broad curve 

 on the lateral surface of the root of the external carotid 

 artery and enters the base of the tongue. The ramus 

 descendens is given off at about the point where it crosses 

 the artery. It has a slender root from the third cervical 

 nerve. 



(e) The cervical portion of the sympathetic trunk begins 

 in the superior cervical ganglion (g. cervicale superius). 

 It lies to the medial side of the vagus ganglion and of the 

 internal carotid artery. The nerves proceeding from the 

 ganglion accompany the branches of the external and 

 internal carotid arteries to the head. 



9. The oral cavity and pharynx. 



The glossopharyngeal nerve and the superior laryngeal nerve 

 and artery may be divided, and. the external carotid, artery with 

 the associated nerves separated from the oesophagus and. trachea. 

 The latter may be displaced downward to a slight extent by 

 dividing the loose connective tissue along the ventral surface of the 

 vertebral column. An incision extending from the oral cavity 

 backward into the oesophagus will expose the internal surface of 

 this portion of the digestive tube sufficiently to make out its 

 features. The incision divides the constrictor pharyngis 

 muscle, a broad band of muscle fibres enclosing the posterior 

 portion of the pharynx. 



For the general relations of the oral cavity see p. 80 and Fig. 41 . 



The divisions are: 



(a) The oral cavity (cavum oris), divisible into the oral cavity 

 proper, and the vestibulum oris, the latter laying between 

 the alveolar processes and teeth on the one hand and the 

 lips on the other. 



(b) The pharynx: its oral portion (pars oralis) continues the 

 oral cavity, and connects it with the oesophagus. Its dorsal, 

 also anterior, nasal portion (pars nas^lis) , or nasopharynx, 

 lies above the soft palate, and receives the posterior aperture 

 of the nose. Its ventral and posterior la ryngeal portion 

 (pars laryngea), not well-defined, contains the aperture of 

 the larynx, the aditus laryngis. 



