442 



TBE DIGESTIVE APPARATUS IN MAiMMALIA. 



lateral channels, limited superiorly by the posterior pillars of the soft palate 

 2. In front of, and beneath this, is the isthmus ofthefdures ; behind and above, 

 the (Bsophajjeal ojienin/i at the bottom of an infundibulum, which may be con- 

 sidered as a special region of the pharynx. 



These seven openings into the pharyngeal cavity give it the appearance of 

 a cross road, into which abut different thoroughfares. It is necessary to note 

 that the air and digestive passages intersect each other here ; and in such a way 

 that, during deglutition, the bolus of food passes over the entrance of the larynx 

 to reach the oesophageal opening. This pecuharity is easily seen by referring to 

 Fig. 250. 



Relations. — Viewed externally, for the study of its connections, it will be 

 found that the pharynx is related, posteriorly, to the guttural pouches, and 

 guttural or retro-pharyngeal lymphatic glands ; laterally, to the great cornu of the 



Fig. 250. 



MEDIAN LONGITUDINAL SECTION OF HEAD AND UPPER PART OF NECK. 



1, Upper lip; 2, premaxilla ; 3, hard palate; 4, tongue; 5, septum nasi; 6, nasal bone; 7, palatine 

 bone; 8, soft palate; 9, pterygoid bone; 10, epiglottis; 11, entrance to Eustachian tube: 12, 

 arytenoid cartilage; 13, cricoid cartilage; 14, oesophagus; 15, frontal bone and sinus; 16, cere- 

 brum; 17, corpus callosum ; 18, cerebellum; 19, sphenoid bone; 20, medulla oblongata, 21, 

 cervical ligament ; 22, spinal cord ; 23, occipital bone ; 24, 24, atlas ; 25, 25, dentata; 26. trachea. 



OS hyoides, the internal pterygoid and stylo-hyoid muscles, the glosso-pharyngeal, 

 great hypoglossal, and superior laryngeal nerves, and the glosso-facial artery. 



Structure. — The walls of the pharynx are composed of a mucous membraney 

 external to which is a, fibroifs and a micscular layer. 



1. Mucous membrane. — This membrane is covered, externally, by a thin 

 layer of yellow elastic fibres, and is much more delicate and less protected by 

 its epithelium than the buccal mucous membrane, of which it is a continuation ; 

 it is continuous with that of the oesophagus, the larynx, the nasal fossae, and 

 the Eustachian tubes. 



Its epithelium is stratified throughout ; but it is thin and ciliated in the upper 

 part, thicker and tesselated on the inferior moiety, which more particularly 

 belongs to the digestive apparatus. 



Everywhere there are racemose glands, though they are most numerous 

 towards the roof of the pharynx. There are also muie follicular glands beneath 



