THE HEAD AND NECK. 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. 
(i) The oral cavity and pharynx. 
he 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 nasalis), or nasopharynx, 
lies above the soft palate, and receives the posterior aperture 
of the nose. Its ventral and posterior laryngeal portion 
(pars laryngea), not well-defined, contains the aperture of 
the larynx, the aditus laryngis. 
