That part or the peritoneum which is reflected from the peripheral surface of the small intestines, and ex tends from them to the lumbar vertebrze, is strictly call ed mesentery, while that part of the same membrane which is reflected from the peripheral surface of the colon, and extends between its great arch and the great curvature of the stomach, is called m•socedon ; and a small portion by which the rectum is attached to the last lumbar vertebra, has the name of meso•ectuni. All these reflected portions of the peritoneum, however, Form only the continuation of the same membrane, pos sess a similar structure, and serve similar purposes. They are all double membranes, and between their folds are contained the large blood-vessels, the mesenteric and lymphatic glands of the belly, the lacteals, and other absorbents.
The mesentery is said to begin at the last flexure of the duodenum, to run obliquely sacral and dextrad along the first, second and third lumbar vertebrae ; the toes°. colon of course commences at about the fourth lumbar vertebra, follows the course of the colon, of which it forms the right and left ligaments, with the broad expan sion between them, that connects the colon with the sto mach, and covers the duodenum and the pancreas.
The course of the Peritoneum, and the manner in which its various doublings pass over the abdominal viscera, are well illustrated by a Plate in the 4th volume of Bell's Anatomy.
the ORGANS of INTEGUMATION To complete our view of all those organs of the hu man body which are common to mankind in general, without taking into consideration the distinguishing cha racters of the sexes, we have only to examine those membranes that form the universal covering of the ex ternal surface, with their appendages. These are usu ally called the Common Integuments, and are here, in conformity with the plan of arrangement to be afterwards explained, denominated the Organs of Intigumation.
The common integuments of the human body consist of the _epidermis, cuticle or scarf skin, the retr MUCOSUM, the true skin, and the cellular membrane ; with those appendages which et; call hair and nail,. Of these we have already treated, of the true skin (see p. 767.) as being the organ of and of the cellular lentbrane. as the general c owlet ting organ of the system. We shall now describe the cuticle, rote inucosum, hair and nails.
The cuticle, epith rinis, or scarf skin, is that ntentbraue which covers the whole excelled surf«, of the body It adheres closely to the pal is beneath, hut may be readly separated from them by maceratioa, by the ap plication of boiling water, or by the action or bliste•,.
(Sec 1'1. XVIII. Fig. 5.) It is of various degree, of thickness in dillerent partsI being thickest in the paints of the Lauds and soles of the feet, esen •hen these are not exposed to much pressure. Exa milled on its peripheral smite, it is found marked with various lines ut a curved direction, and generally paral lel to each other. These are mist reit:ark:tide in the points of the lingers. Interspersed uith these lines. are numerous pores, which appear to correspond with those on the true skin, and are most evident about the nose, ears, palms of the hand, and soles of the feet When separated from the adjacent membranes, the cu ticle is of a white colour, and, except in the palms and soles, it is transparent. It appears to possess but VCI'y little extensibility, scarcely any elasticity, and is perfectly insensible.
In general the cuticle is composed of a single layer. but where it is very thick, it may be easily separated in to several layers and frequently one of these peels off and discovers the subjacent /annna.
Authors are not agreed respecting the nature of this membrane. Most anatomists consider it as an inorganic substance, merely spread over the surface of the body, but having no vascular connection with the parts be neath. Others, among whom are Dr William Hunter and Mr Cruikshank, have believed it to be organized, though they cannot prove its organization. It is certain that no vessels or nerves can be discovered running along the cuticle, though, on detaching this membrane from the skin, small filaments are observed, which arc supposed to be the exhalants that open by the cuticular pores. Some have considered it as an exudation from the cutaneous vessels, hardened by exposure to the air ; but this is rendered improbable, if it be not entirely con troverted, by the circumstance that the fetus in utcro is covered with a cuticle.
It is well known that the cuticle, when removed, is •e produced, and that it is thickened, or its layers are in creased by the application of pressure. In this way are produced those horny excrescences which we call corns.
It is generally supposed that the fine and delicate membrane %%hich covers the lips, lines the interior of the mouth and all the ca‘ities that communicate with the surface, and arc invested by inticous membranes, is merely a continuation of the cuticle, though, from its greater thinness, it is distinguished by a different name viz. (pi/he/hint.