THE CAVITY OF THE MOUTH. 665 



The TONSIL is an oval body, of variable size, placed above the Tonsil is 

 iv< t of the tongue, in a recess between the anterior and posterior pi i lars of 

 pillars of the soft palate. Externally it is covered by the superior fauces : 

 constrictor muscle, and is a little above the angle of the lower jaw. 



The surface of the tonsil is marked by apertures, which lead into structure, 

 crypts, or recesses, lined by mucous membrane. Its substance 

 consists mainly of lymphoid tissue, partly diffused, and partly 

 collected into follicles set round the walls of these recesses. A similar Pharyngeal 

 collection of lyniphoid tissue stretches across the posterior wall of to 

 the pharynx, between the openings of the Eustachian tube, and is 

 known as the pharyngeal tonsil. 



The arteries of the tonsil are numerous, and are derived from the Vessels, 

 facial, lingual, ascending pharyngeal and internal maxillary branches 

 of the external carotid. Its veins have a plexitorm arrangement on and nerves, 

 the outer side. Nerves are furnished to it from the fifth and glosso- 

 pharyngeal. Its lymphatics join the deep cervical glands. 



The MUCOUS MEMBRANE OF THE PHARYNX is continuous in front MUCOUS 

 with the lining of the nose, mouth and larynx. A fold encloses the 

 muscles and glands of the soft palate, from which the membrane 

 descends on each side over the tonsil to the tongue. It is also pro- 

 longed by the Eustachian tube to the tympanum ; and below, it is 

 continued into the oesophagus. It is provided with numerous glands ; 

 mucous glands in the upper part of the pharynx, and on both sur- 

 faces, but especially the upper, of the soft palate. Another collec- 

 tion of glands (arytenoid) is enclosed in the fold of mucous mem- 

 brane bounding the opening of the larynx on each side. The epithelium, 

 epithelium is columnar and ciliated above the soft palate, but scaly 

 and strati tied below that part. 



The (ESOPHAGUS. This tube is much smaller than the pharynx, Beginning 

 and the walls are flaccid. It consists of two layers of muscular g f u * sopba 

 fibres, with a lining of mucous membrane. The external layer is TWO layers 

 formed of longitudinal fibres, which begin opposite the cricoid b m "! cular 

 cartilage by three bundles, an anterior and two lateral ; the former outer ion- 

 is attached to the ridge at the back of the cartilage, and the others & 

 join the inferior constrictor. The internal layer is formed of circular pd inner 

 fibres, which are continuous with those of the inferior constrictor. 

 The structure of the oesophagus is described more fully in the 

 dissection of the thorax. 



The CAVITY OF THE MOUTH. The cavity of the mouth extends Mouth, 

 from the lips in front to the anterior pillars of the fauces behind. 

 Its boundaries are partly osseous and partly muscular, and its size 

 depends upon the position of the lower jaw-bone. When the lower form, 

 jaw is moderately removed from the upper, the mouth is an oval 

 cavity with the following boundaries. The roof, concave, is consti- 

 tuted by the hard and soft palate, and is limited in front and on the 

 sides by the arch of the teeth. In the floor is the tongue, surrounded 

 by the arch of the lower teeth ; and beneath that body is the sub- 

 lingual gland on each side. Each lateral boundary consists of the 

 cheek and the ramus of the lower jaw ; and in it, uear the second 



