PHYSIOLOGICAL ANATOMY OF THE STOMACH. 227 



the involuntary, pale, or unstriped variety. These fibres, called sometimes muscular 

 fibre-cells, are very pale, with faint outlines, fusiform or spindle-shaped, and contain each 

 an oval, longitudinal nucleus. They are very closely adherent by their sides, and are so 

 arranged as to dovetail into each other, forming sheets of greater or less thickness, 

 depending upon the number of their layers. The muscular coat of the stomach varies in 

 thickness in different animals. In the human subject, it is thickest in the region of the 

 pylorus and is thinnest at the fundus. Its average thickness is about -^ of an inch. In 

 the pylorus, it is from ^ to T ^ of an inch thick, and in the fundus, from ^ to -% of an inch. 

 The muscular fibres exist in the stomach in two principal layers ; an external, longi- 

 tudinal layer and an internal, circular layer, with a third layer of oblique fibres extending 

 over the great pouch only, which is internal to the circular layer. The direction of the 

 fibres in these layers can generally be seen in a stomach which has been dried and inflated. 

 The longitudinal fibres are continued from the oesophagus and are most marked over the 

 lesser curvature. They are not continued very distinctly over the rest of the stomach. 

 The circular and oblique fibres are best seen when the organ has been everted and the 

 mucous membrane carefully removed. The circular layer is not very distinct to the left 

 of the cardiac opening, over the great pouch, but in other parts it is tolerably regular. 

 Toward the pylorus, the fibres become more numerous, and, at the opening into the 

 duodenum, they form a powerful muscular ring, which is sometimes called the sphincter 

 of the pylorus, or the pyloric muscle. At this point they project considerably into the 

 interior of the organ and cease abruptly at the opening into the duodenum, so as to form 

 a sort of valve, presenting, when contracted, a flat surface looking toward the intestine. 

 The oblique layer takes the place, in great part, of the circular fibres over the great 

 pouch. It extends obliquely over the fundus from left to right and ceases at a distinct 

 line extending from the left margin of the oesophagus to about the junction of the middle 

 with the last third of the great curvature. This anatomical fact is interesting, for it 

 is at about the point where the oolique layer of fibres ceases that the stomach becomes 

 constricted during the movements which are incident to digestion, dividing the organ into 

 two tolerably distinct compartments. 



FIG. 54. Longitudinal fibres of the stomach. (Sappey.) 



1, lesser curvature ; 2, 2, greater curvature ; 3, greater pouch ; 4, lesser pouch ; 5, 6, 6, lower end of the oesophagus ; 7,T, 

 pylorus ; 8, 8, longitudinal fibres at the lesser curvature ; 9, fibres extending over the greater curvature ; 10, 10, 

 a very thin layer of longitudinal fibres over the anterior surface of the stomach; 11, circular fibres seen through 

 the thin layer of longitudinal fibres. 



