THE (ESOPHAGUS. 



379 



right, to a fissure in the superior border of the liver, and is enveloped by the 

 peritoneum. 



Interior. Internally, the canal whose course and relations we have just 

 studied presents nothing of interest ; and it only requires to be remarked, 

 that its walls are always shrunken and in contact when food is not passing 

 between them. 



STRUCTURE. The oesophagus has two tunics : a mucous and a muscular. 



The mucous membrane is continuous with that of the pharynx and the 

 stomach ; it is white, and shows numerous longitudinal folds which allow 

 the canal to dilate. It adheres but loosely to the muscular coat, on which 

 it can glide with the greatest facility. It has a thick, resisting, stratified, 

 tesselated epithelium, an unstriped muscular layer, and some racemose 

 glands. 



Fig. 179. 



PECTORAL CAVITY AND MEDIASTINUM, SHOWING THE COURSE OF THE TRACHEA 

 AND (ESOPHAGUS. 



(A third or middle coat is sometimes mentioned by anatomists ; it is 

 composed of the tissue connecting the latter tunic with the one to be next 

 described.) 



The muscular coat commences at the posterior part of the pharynx by 

 the aryteno-pharyngei muscles, and by two small superficial bands which 

 are detached from the posterior portion of the crico-pharyngei muscles. 

 This tunic is formed of superficial longitudinal fibres, often assembled in 

 fasciculi ; and of a deeper series of spiral or circular fibres, which, towards 

 the inferior extremity of the canal, intercross in an almost inextricable 

 manner. This muscular layer in the cervical, and for a great part of the 

 thoracic portion of the oesophagus, has the red colour of voluntary muscles ; 

 but it becomes white, like the involuntary fibres, after the conduit enters 

 the mediastinum, and acquires considerable thickness and marked rigidity. 

 It is to be noted that this arrangement of the muscular tunic is especially 



