460 THE DIGESTIVE APPARATUS IN MAMMALIA. 



plane, and finish by becoming mixed so intimately with these, that towards the 

 tuberosity formed by the left extremity it is impossible to distinguish them. By 

 their aggregation around the pylorus, they constitute the sphincter {ov pyloric 

 valve) which envelops that orifice. 



The deep plane (Fig. 261, a), like the first, is specially destined for the left 

 sac, and cannot be properly studied except in an averted 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 the extremities of which are lost on the faces of 

 the organ, where some of them become continuous with 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 



Fig. 261. 



Fig. 262. 



MUSCULAR FIBRES OF THE STOMACH 

 (external and middle LAYERS). 



A, Fibres of the external layer enveloping 

 the left sac; B, fibres of the middle 

 plane in the right sac ; C, fibres of the 

 pylorus. 



deep and middle muscular layer ex- 

 posed BY removing the MUCOUS MEM- 

 BRANE FROM AN EVERTED STOMACH. 



A, Deep layer of fibres enveloping the left 

 sac ; B, fibres of the middle plane which 

 alone form the muscular layer of the 

 right sac ; C, fibres of the pylorus. 



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. 261 and 262 will show : 

 1. That the right sac has only a singular muscular plane. 2. That, on the con- 

 trary, the left sac has three, all of which concur in propelling the ahment that 

 has accumulated in the left, or oesophageal reservoir, into the right, or true 

 stomach. 



3. Mucous membrane. — Independently of the general characters noted 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, 

 but extremely numerous in the right. In this region they are separated from 



