230 



STRUCTURE OF THE (ESOPHAGUS. 



[Structure of the (Esophagus. The walls of the cesophagus are composed of four coats 

 mucous, sub-mucous, muscular, and fibrous (fig. 171). 



(1) The mucous coat is firm, and is thrown into longitudinal folds, which disappear when the 

 tube is distended. It is lined by several layers of stratified squamous epithelium. The 

 membrane itself is composed, especially at its inner part, of dense fibrous tissue, which projects, 

 in the form of papillae, into the stratified epithelium. The papillae are present in the child, but 

 are largest in old people. At its outer part is a continuous longitudinal layer of non-striped 

 muscle, the muscularis mucosae. The layer consists of small bundles of non-striped muscle 

 separate from each other. 



(2) The sub-mucous coat is thicker than the foregoing, and consists of loose connective- 

 tissue, with the acini of small mucous glands imbedded in it. The ducts pierce the muscularis 

 mucosae to open on the inner surface of the tube. 



(3) The muscular coat consists of an inner, thicker, circular, and an outer, thinner, longi- 

 tudinal layer of non-striped muscle, commencing on a level with the cricoid cartilage. In man 

 the upper third of the gullet consists of striped muscular fibres. (4) Outside the muscular coat 



Excretory duct. 



Sub-mucosa. 



' /Circular mus 

 o | cular fibres, 



Fig. 171. 

 Transverse section of part of the cesophagus. 



is a layer of fibrous tissue with elastic fibres. The structure of the muscular coat of the 

 cesophagus varies much in different animals. In the rabbit, in the first quarter of its length, 

 it has two layers, but below this there are three layers, i.e., a circular between an outer and an 

 inner longitudinal layer, while the non-striped fibres are confined to the lowest quarter of the 

 tube.] 



[Nerve-Plexuses. As in the intestine, there are two plexuses of nerves with ganglia ; one in 

 the sub-mucous coaj (Meissners) and the other between the two muscular coats (Auerbactis), 

 which are continuous with those in the stomach and intestine. Blood-vessels and numerous 

 lymphatics lie in the mucous and sub-mucous coats.] 



157. MOVEMENTS OF THE STOMACH. Position. When the stomach 

 is empty, the great curvature is directed downwards and the lesser upwards ; but 

 when the organ is full, it rotates on an axis running horizontally through the 

 pylorus and cardia, so that the great curvature appears to be directed to the front 

 and the lesser backwards. 



Arrangement of the Muscular Fibres. The non-striped muscular fibres of the stomach are 

 arranged in three directions or layers, an outer longitudinal continuous with those of the 

 cesophagus. This layer is best developed along the curvatures, especially the lesser. At the 

 pylorus the fibres form a thick layer, and become continuous with the longitudinal fibres of the 

 duodenum. The. circular fibres form a complete layer ; at the pylorus they are more numerous, 

 and constitute the sphincter-muscle or pyloric valve ; whilst at the cardia (inlet), such a 

 muscular ring is absent. The innermost oblique or diagonal layer is complete. 



The Movements of the Stomach are of two kinds : (1) The rotatory or churn- 

 ing movements, whereby the parts of the wall of the stomach in contact with the 



