SPLANCHNOLOGY 145 



The submucosa, connects the mucous and muscular coats and 

 the muscularis layer throws the mucous membrane into folds. 



Outside the muscularis mucosa there is another layer (Fig. 32, 

 A), of simple tubular glands, grouped in lobules, and lined ~By~ 

 cuboidal cells and separated from each other by clefts. These 

 tubular glands converge toward the center and open into the same 

 cavity. 



The middle muscular coat can be divided into three layers: 

 two thin, longitudinal layers, and a thick, circular layer interposed 

 between the other two. 



Function. The function of the proventriculus appears to be 

 to soak the food with a secretion. The secretion from the proven- 

 triculus is similar to that produced by the fundus glands of the 

 stomach of mammals. It contains acid and a ferment-pepsin. 



The Gizzard (Fig. 31, No. 18). Location. The gizzard, or mus- 

 cular stomach, occupies a portion of the central part of the abdominal 

 cavity (Fig. 33, No. 4). It lies slightly to the left and just behind 

 the liver, the proventriculus, and the spleen, and rests upon a mass 

 of intestines. The gizzard communicates at its anterior portion 

 with the proventriculus and with the duodenum. These openings 

 are close together. The gizzards of a large number of hens of 

 average size averaged in weight as follows: full, 0.215 pound; 

 empty, 0.126 pound. The gizzard stands perpendicularly and 

 somewhat obliquely in the abdominal cavity. 



Shape. In shape the gizzard is roundish, flattened laterally. 



Structure. The walls of the gizzard are very thick and are made 

 up of three coats: mucous, muscular, and serous. 



The cavity of the gizzard is covered by a thick skin-like structure 

 possessing a heavy stratified squamous epithelial layer which is 

 thrown somewhat into ridges (Fig. 32, B). This membrane becomes 

 thinnest near the edges. 



The mucous membrane, being cornified and readily detachable, 

 is by some anatomists considered as a special membrane (Fig. 

 37, B). 



At the pyloric opening there is a valve formed by a fold of the 

 mucous membrane, which prevents grit and large particles of food 

 from passing out of the gizzard. 



On each side it has a powerful fleshy muscle, the muscularis 

 lateralis. These musculares laterales are hemispherical, consist of 

 very closely packed fibers extending transversely, and are attached 

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