390 THE DIGESTIVE APPARATUS IN MAMMALIA. 



they constitute the sphincter (or pyloric valve) which envelops that 

 orifice. 



The deep plane (Fig. 186, A), like the first, is specially destined for 

 the left sac, and cannot be properly studied except in an everted stomach 

 deprived of its mucous membrane. Much thicker than the superficial plane, 

 it yet, in its general arrangement, much resembles it. Thus, its fasciculi 

 present loops which embrace the left cul-de-sac, and whose extremities are 

 lost on the faces of the organ, where some of them become continuous with 



Fig. 185. Fig. 186. 



MUSCULAR FIBRES OF THE STOMACH ; DEEP AND MIDDLE MUSCULAR LAYERS EX- 



EXTERNAL AND MIDDLE LAYERS. POSED BY REMOVING THE MUCOUS MEM- 



A, Fibres of the external layer enveloping BRANE FROM AN EVERTED STOMACH. 

 the left sac ; B, Fibres of the middle plane A, Deep layer of fibres enveloping the left sac ; 

 in the right sac ; C, Fibres of the ceso- B, Fibres of the middle plane which alone 



phagus, t form the muscular layer of the right sac ; 



C, Fibres of the oesophagus. 



the circular fibres. The loops nearest the oesophagus embrace the stomachal 

 opening of that canal like a cravat. It is to be remarked that the fibres 

 of this deep layer intersect those of the superficial plane ; the former 

 passing from the left to the right sac, in inclining downwards towards 

 the great curvature, while the latter are directed to the right and slightly 

 upwards. 



From this arrangement it results, as a glance at Figs. 185, 186 will show : 

 1, That the right sac has only a single muscular plane ; 2, That, on the 

 contrary, the left sac has three, all of which concur in propelling the 

 aliment that has accumulated in the left or oesophageal compartment into 

 the right, or true stomach. 



3. Mucous membrane. Independently of the general characters notified 

 in the interior of the stomach, it has to be remarked that the gastric mucous 

 membrane is united to the preceding tunic by an expansion of connective 

 tissue ; though it adheres but feebly throughout the right sac, especially 

 towards the greater curvature, where it is thickest ; and that it has no ridges 

 in the left sac, though in the right they are always present, even when the 

 organ is inflated. 



On the surface of this membrane are seen microscopical apertures (alveoli), 

 the orifices of the excretory ducts of glands; these are rare in the left sac, 



