556 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. 



tion as the gland-sacs diminish in size. The muscularis externa 

 consists of three layers, because at the entrance of tha oeso- 

 phagus into the digestive stomach, the submucous tissue disap- 

 pears. These are thicker at the point, corresponding to the space 

 between the extremities of two adjoining saccular glands, than 

 in those places where they are directly attached to their convex 

 external portion. At the point of transition of the glandular 

 stomach into the intermediate segment the fasciculi of the outer 

 layers decrease in number and size, but those of the middle 

 and internal layers augment, so that in the intermediate seg- 

 ment the external muscular tunic consists only of an external 

 circular and an internal longitudinal layer. 



In the mucous membrane of the intermediate portion of 

 the fowl, straight, closely arranged tubular glands are met with, 

 the extremities of which are somewhat narrower than their ori- 

 fices, and are lined with spheroidal cells which gradually change 

 as they pass upwards into the columnar epithelium of the sur- 

 face. The tissue of the mucous membrane forms externally to 

 the extremity of the tubes a thin, moderately dense layer, con- 

 taining a variable quantity of lymph corpuscles, vessels, and 

 nerves. 



The muscular tunic consists of an internal longitudinal and 

 an external circular layer ; amongst the fasciculi of the latter 

 are a few groups of fat cells. 



In the intermediate portion the secretion of the glands be- 

 comes hardened into the form of a homogeneous thin layer 

 covering the surface of the epithelium, through which ho- 

 mogeneous bands are prolonged in a vertical direction from 

 the interior of the tubes. This layer investing the surface ac- 

 quires a peculiar significance in the true muscular stomach or 

 gizzard, where it forms a peculiar horny layer, at first thin, but 

 gradually increasing in thickness as it descends, and when ex- 

 amined in thin sections with transmitted light, presents a deep 

 yellow colour. The surface of the mucous membrane invested 

 with this horny and, by reflected light, dark brown layer, 

 forms at the commencement of the gizzard numerous tolerably 

 regularly arranged corrugations, which however diminish in 

 number and height, but increase in breadth downwards. The 

 horny layer everywhere follows these elevations ; with the in- 



