TEE (ESOPHAGUS. 



449 



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. 



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

 posed of the tissue connecting the latter tunic with the one to be next described.) 



The muscular roat comnK'nces at the posterior part of the pharynx by the 

 arytmo-msophayml and superior lomjitudinnl msophafieal mimles (Fig. 251). The 

 aryteno-cesophageal muscle is an extremely thin, small band in Solipeds, situated 

 on the posterior border of the arytsenoid cartilage, at the commencement of the 

 oesophagus, where its fibres disappear. To expose this muscle — which represents 

 the inferior longitudinal a'sophageal of some authorities, the oesophagus should 

 be turned forwards on the upper surface of the pharynx. 



The superior longitudinal ostiop/iageal muscle is a small superficial band, the 



Fig. 255. 



PECTORAL CAVITY AND MEDIASTTNUM, SHOWING THE COURSE OF THE TRACHEA 

 AND (ESOPHAGUS. 



A, Anterior mediastinum ; B, posterior mediastinum; c, the heart iiiv\ peiicardium in the middle 

 part of the mediastinum; D, diaphragm; E, trachea; F, oesophagus. 



fibres of which leave the base of the fibrous triangle that occupies the posterior 

 face of the pharynx, to disappear on the surface of the oesophagus, where some 

 of them form loops at different elevations. 



To these muscles at the commencement of the oesophagus, must be added 

 the crico-asophageal, which leaves the deep face of the crico-pharyngeus to pass 

 to the border of the oesophagus, where its fibres proceed above and below that tube, 

 in joining those of the muscle of the opposite side. This muscle compresses the 

 oesophagus at its commencement, in the same way as Wilson's muscle acts upon 

 the urethra. 



The remainder of this muscular 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 almost the red colour of voluntary 



