THE FACE, MOUTH AND PHARYNX 



191 



branches from the sympathetic trunk. The sensory portion of the plexus is 

 distributed to the whole of the pharyngeal mucous membrane, except that 

 covering the roof and the adjoining areas of the lateral walls, which is 

 supplied by a branch from the spheno-palatine ganglion (p. 233). 



The Oral and Laryngeal Portions of the Pharynx lie behind 

 the mouth, the dorsum of the tongue, and the larynx. Later- 

 ally they are related to the great vessels of the neck, and pos- 

 teriorly they are separated from the bodies of the upper cervical 

 vertebrae by the retro-pharyngeal and prevertebral layers of 

 fascia and the longus colli muscles. A retro-pharyngeal abscess 

 (p. 114) produces a swelling of the posterior pharyngeal wall 

 which may obstruct the passage of air during respiration, causing 

 symptoms not unlike those associated with adenoids and hyper- 

 trophied palatine tonsils (Fig. 37). 



Prosencephalon 



Median nasal 

 process 



Eye 

 Stomatod?eum 



Globular process 



Olfactory pit 



FIG. 55. The Development of the Face. 



Development of the Face and Mouth. About the thirteenth 

 day a depression appears on the ventral surface of the embryo 

 just behind the anterior cerebral vesicle. This is the stomodceum 

 or primitive mouth, and it is separated from the foregut by the 

 bucco-pharyngeal membrane, which soon breaks down. An 

 elevation appears in the middle line of the roof of the stomodceum 

 the fronto-nasal process and the olfactory pits lie on each side 

 of it. These pits form shallow grooves running backwards in 

 the roof of the primitive mouth, and they become bounded in 

 front by elevations produced by the lateral and median nasal 

 processes, both of which are derived from the fronto-nasal 

 process. The mandibular arches (p. 148) unite to complete the 



