310 ANATOMY OF THE RABBIT 



The fibres composing the ramus descendens do not originate in 

 the hypoglossal nucleus in the brain but are derived from the most 

 anterior cervical nerves and are only secondarily included within the 

 sheath of the hypoglossal. 



(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 caro- 

 tid 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. If a probe is inserted from the oral cavity backward into 

 the oesophagus and an incision through the lateral wall is made 

 following this guide, the internal surface of this portion of the 

 digestive tube will be exposed sufficiently for the study of its 

 features. The incision divides the constrictor pharyngis muscle, 

 a broad band of muscle fibres enclosing the posterior portion of the 

 pharynx. 



The constrictor pharyngis has three heads of origin, not readily distinguished : 

 (a) a very fine band from the base of the external acoustic meatus, (b) a larger 

 mass from the tip of the medial lamina of the pterygoid process, and (c) a delicate 

 band attached in the soft palate. 



For the general relations of the oral cavity see p. 99 and Fig. 52. 



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

 cavity proper, and the vestibulum oris, the latter lying 

 between the alveolar processes and teeth on the one hand 

 and the lips and cheeks on the other. 



(b) The pharynx comprises an oral portion (pars oralis), con- 

 tinuing the canal of which the first division is the oral 

 cavity and connecting the latter with the oesophagus, and 

 a dorsal and anterior nasal portion (pars nasalis) or naso- 

 pharynx, which lies above the soft palate, and receives the 

 posterior aperture of the nose. Its ventral and posterior 



