D. THE STOMACH, BY E. KLEIN. 'i^'l 



structure. Its left half may be regarded as a continuation of 

 the oesophagus, whilst the right half forms the stomach in the 

 proper sense of the word. The mucous membrane lining the 

 latter portion is of a reddish-brown colour on the surface, like 

 that of the fundus of the above-described animals. The two 

 halves are divided by a fold which commences at the right 

 extremity of the oesophagus that here enters the middle of the 

 small curvature, and is so arranged as to open only into the left 

 half ; the communication of its orifice with the right half of the 

 stomach being capable of entire occlusion by this arcuate fold. 



The wall of the stomach is considerably thinner in the left 

 half than in the right, at the cost both of the mucosa and of 

 the muscularis externa. It is thinnest in the csecal dilatation 

 directed upwards, which the left half of the stomach forms at 

 the junction of the large and small curvature. The left half 

 of the stomach may also, from its structural characters, be re- 

 garded as a continuation of the oesophagus. 



The laminated pavement epithelium increases in thickness' 

 from left to right to the summit of the fold, the height of 

 which is about 1*5 millimeter, but again decreases on the right 

 side, the uppermost cells first disappearing by becoming fused 

 into a homogeneous layer; then the middle polyhedric cells 

 vanish, whilst the deepest cells, which are arranged on the fold 

 in the form of palisades and are cylindrical, increase in height, 

 and commencing from the middle of the right side of the fold, 

 cover the mucous membrane as a simple columnar epithelium. 



The mucosa, which becomes stronger in passing towards the 

 fold from the right, soon begins to form conical vascular pa- 

 pillae, which are at first small, but with the increasing thick- 

 ness of the pavement epithelium towards the summit of the 

 fold increase in height. 



The muscularis mucosse exhibits the most important modifi^ 

 cations. It is to it that the existence of the fold is essentially 

 due. The nearer the fold is approximated, the more distinctly 

 does it become differentiated into internal circular and the 

 external longitudinal layers. 



The former, rapidly increasing in thickness, ceases after at- 

 taining its greatest thickness at the summit of the fold, only 

 the uppermost fasciculi remaining, which are now continued 



