502 SPECIAL HISTOLOGY. 



ness of 0-36-0'45 of a line is due, to the extent of about 0-1-0-12 of a line, 

 to its laminated, tessellated epithelium, Avhich presents the same structure 

 as in the oral cavity, with the exception, however, that the actual epithe- 

 lial plates constitute about a moiety of the whole, and, after a short mace- 

 ration, or, as frequently happens in the dead subject, spontaneously, 

 may be readily stripped off in large white sheets, either alone, or accom- 

 panied by adherent portions of the deeper layers. The proper mucous 

 membrane, measuring on the average 0*3 of a line, possesses numerous 

 conical papilhv of 0-04-0-05 of a line in length, and consists of ordinary 

 connective tissue, with fine elastic fibres, among which, however, as 

 Briicke and I have ascertained, a great quantity of longitudinal bundles 

 of smooth muscles, and in addition, more isolated groups of ordinary fat 

 cells and small racemose mucous glands, may be observed. 



The oesophagus is moderately provided with lymphatics and blood- 

 vessels; the latter send loops into the papillce and form at their bases, 

 a not very wide network, like that in the pharynx. Nerves may also 

 be met with in considerable numbers in the mucous membrane, contain- 

 ing fine fibres of 0-0012-0-0015 of a line, but I have not yet succeeded 

 in tracing them into the papillce, nor in observing divisions, nor the 

 modes in which they terminate. 



Literature. — C. Th. Tourtual, "Neue Untersuchungen iiber den Bau 

 des Menschlichen Schlund-und Kehlkopfes," Leipzig, 1846. 



OF THE ALIMENTARY CANAL. 



§ 146. Those parts Avhich constitute what may, more strictly speaking, 

 be called the alimentary canal, are the least fixed of all which compose 

 the alimentary tract and are almost invariably attached by special mem- 

 branous bands — the mesentcria — in the great cavity of the abdomen, 

 lined by the peritonaeum. With the exception of a small portion of the 

 rectum, the walls of the alimentary canal consist everywhere of three 

 tunics: sl serous — the peritonceum ; a muscular — consisting of two or 

 even three layers ; and a mucous membrane, the latter containing a 

 great number of glandular structures, which may be divided into three 

 groups, racemose mucous glands, tubular glands, and closed follicles. 



§ 147. The peritoticEum is much thicker in its external or parietal, 

 than in its internal or visceral layer (in the former case 0-04-0-06, in 

 the latter 0-02-0-03 of a line), though its structure is essentially the 

 same in each locality. It consists principally of connective tissue with 

 distinct, variously interwoven bundles, and abundant reticulated elastic 

 fibres, which are coarser in the parietal lamina. A loose subserous con- 

 nective tissue, containing more or less fat, unites the peritonaeum with 

 the other organs, or, as in the mesenteric folds, connects its layers 

 together ; under the visceral lamina, however, it is very little developed 

 except in certain localities [colon, appendices epiploicoi), and in certain 



