THE STOMACH. 399 



Structure. The serous layer is a dependency of the peritoneum, and offers nothing 

 particular ; it does not completely cover the anterior face. 



The muscular tunic is much fasciculated, and thin. 



The mucous membrane is remarkable for the thickness of its stratified pavement 

 epithelium ; all the leaves are formed by two layers of this membrane, laid one against the 

 other ; and as their structure is interesting, we will notice it. 



The principal leaves are composed of this duplicature of mucous membrane, and two 

 layers of muscular fibres between ; these layers are opposite each other at the commence- 

 ment of the leaf, and separated by a transverse vessel ; in the remainder of their extent 

 they are kept apart by the vessels that pass towards the border of the leaf. Their fibr< s 

 are detached from the surface of the muscular tunic and, at certain points, from its deep 

 layer. In the smaller leaves there appears to be only one layer of muscular fibres ; on 

 all the leaves are various-sized papillae, the smallest of which are like a grain of millet, 



Fig. 195. Fig. 196. 



V-- 



SECTION OF A LEAF OF THE OMASUM. LONGITUDINAL SECTION OF A LARGE PA- 



1, 1, Muscular planes ; , vessel ; 2, Epithe- PILLA FROM THE OMASUM, SHOWING 

 Hum ; 3, 3, Small-sized papilla?, round NERVE-CELLS IN ITS INTERIOR. 

 and hard. 



and have for base a mass of condensed connective tissue, whose superficial fibres form a 

 kind of shell (Fig. 195) ; the largest are club-shaped. They receive blood-vessels, and 

 we have found in the connective tissue, elements with a somewhat irregular outline, pro- 

 vided with nuclei, which we considered to be nerve-cells (Fig. 196.) 



ABOMASUM (REED or RENNET. Figs. 192, 193). Situation Form Relations. The 

 abomasum stands next to the rumen for capacity. It is a pyriform reservoir, curved on 

 itself, elongated from before to behind, and situated behind the omasum, above the right 

 sac of the rumen. On the right it touches the diaphragm and the hypochondriac; on 

 the left it is related to the rumen. The greater curvature, turned downwards, receives 

 the insertion of the great omentum. The lesser curvature, inclined upwards, gives 

 attachment to the serous band already noticed when speaking of the great curvature of 

 the omasum. Its base is in contact with the cul-de-sac of the reticulum, and is separated 

 from the omasum by the constriction in the form of a thick neck, which corresponds tc 

 the communicating orifice of the two stomachs. Its point, directed upwards and back- 

 wards, is continued by the duodenum. 



Interior. This being the true stomach of Ruminants, the mucous membrane lining 

 its interior acquires all the characters which distinguish that of the stomach of the 

 Carnivora, or that of the right sac of the Horse's stomach. It is soft, spongy, smooth to 

 the touch, vascular, red-coloured, covered by a thin epithelium, and provided with 

 numerous glands for the secretion of the gastric juice. Thinner than in monogastric 

 animals, this tenuity is compensated for by a much greater extent of surface, which is 

 still further increased by numerous lamellar folds. These latter are analogous in con- 

 stitution to those of the omasum, cross in a very oblique manner the great axis of the 

 abomasum, and altogether affect a kind of spiral arrangement. 



The abomasum has two apertures : one, situated at its base, opens into the omasum ; 

 the other, placed opposite to the first, and much narrower, is the pylorus, which is 

 circumscribed, as in the other animals, by a muscular ring. 



Structure. The serous membrane is continuous with the omenta which abut on the 

 great and lesser curvatures of the viscus. The muscular layer is of the same thickness 

 as in the omasum. The internal tunic has already been noticed. 



FUNCTIONS OF THE STOMACH IN RUMINANTS. We cannot pretend to give here a 

 complete history of the phenomena of rumination, but must confine ourselves to describe 

 in a few words what are the principal attributes of each gastric dilatation. 



