210 DIGESTION. 



the muscular fibres forming the middle coat are of the invol- 

 untary, pale, or unstriped variety. These fibres, called some- 

 times muscular fibre-cells, are very pale, with faint outlines, 

 fusiform or spindle-shaped, and presenting an oval longitu- 

 dinal nucleus. They are very closely adherent by their 

 sides ; and are so arranged as to dove-tail into each other, 

 and form 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 sub- 

 ject, it is thickest in the regio'n of the pylorus and is thin- 

 nest at the fundus. Its average thickness is about ^\ of an - 

 inch. In the pylorus, it is from T ^ to y 1 ^ of an inch thick, 

 and in the fundus from ^ to ^ of an inch. 1 



The muscular fibres exist in the stomach in two princi- 

 pal layers ; an external longitudinal layer and an internal cir- 

 cular layer, with a third layer of oblique fibres extending only 

 over the great pouch, 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 in 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 is tolerably 

 regular. Toward the pylorus, the fibres become more numer- 

 ous, and at the opening into the duodenum, form a powerful 

 muscular ring, which is sometimes called the sphincter of 

 the pylorus, or the pyloric muscle. At this point they pro- 

 ject considerably into the calibre 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 



1 KOLLIKER, Manual of Human Microscopic Anatomy, London, 1860, p. 316. 



