316 FERITONEAL COAT OF ALIMENTARY CANAL, [sect. 147. 



principally of connective tissue, in distinct, variously decussating 

 bundles, and numerous networks of elastic fibres, which are thicker 

 in the parietal portion. A loose subserous connective tissue, with 

 more or less fat, connects the peritoneum with subjacent parts, 

 or holds its layers together where the membrane forms folds, as 

 in the mesentery. Under the visceral layer, however, the sub- 

 serous connective tissue is, except in certain places (colon, ap- 

 pendices epiploic^), but little developed, or even not at all 

 demonstrable, as in certain peritoneal ligaments. The free surface 

 of both peritoneal lamelhe is covered by a simple pavement- 

 epithelium, whose slightly flattened, polygonal, nucleated cells 

 amount on an average to o'oi'" in diameter, and are so firmly 

 united together, that the free surface of the serous membrane 

 appears perfectly smooth, and, from its being always moistened, 

 also shining. 



The blood-vessels of the peritoneum are, in general, few. They 

 are most numerous in the omenta and in the visceral layer, also 

 in the subserous tissue, in which latter alone, lymphatic vessels 

 have, hitherto, been demonstrated. The nerves also are not very 

 numerous; they may be shown especially in the omentum, the 

 mesentery, on the diaphragm, and the spleen, and in the hepatic 

 ligaments, to which they may be traced from the phrenic, in 

 company with the arteries. 



§ 147. Muscular Coat. — All parts of the alimentary tract, from 

 the stomach to the rectum, possess a special muscular coat, which, 

 however, does not everywhere present the same conditions. 



In the stomach, the muscular coat is not everywhere equally 



thick; at the fundus it is very thin (£'" to '■\'"), in the middle, 



about Y'} m ^ ie pyloric region, %" or even 1" thick. It consists 



of three incomplete layers, viz., 1st, most externally, longitudinal 



fibres : these consist of fibres radiating from the longitudinal fibres 



of the oesophagus (those on the small curvature extending to the 



lylorus, whilst the others run out free upon the anterior and 



>osterior wall of the stomach and upon the upper side of the 



undus), and of independent fibres upon the right half of the 



itomach, from which part, tensely stretched, they pass upon the 



duodenum : 2nd, circular fibres, which pass from the right side of 



the cardia onwards as far as the pylorus, where they are thickest, 



and form the sphincter pylori, as it is termed : 3rd, oblique fibres, 



most internally, which, being connected with certain circular 



bundles at ike fundus, embrace that part in form of loops, and 



