198 GENERAL ANATOMY. 



mucous membrane, has not a regularly aereolar disposition 

 like that of the cutaneous dermis; it is rather spongy or 

 fungous. Blood-vessels and lymphatics abound in it. Its 

 nerves generally arise from the great sympathetic and the par- 

 vagum: at all the natural orifices, the mucous membrane is 

 supplied with nerves from the medulla spinalis. 



274. The colour of the mucous membrane varies from 

 white to red, and besides the intermediate shades, it presents 

 other differences of colour. This colour is owing, at least in 

 a great measure, to the blood which circulates through its 

 thickness, for asphyxia or syncope, either imparts a brown tint 

 to, or instantly deprives of all colour, the parts of this mem- 

 brane which from their situation are visible. Its consistence 

 is, in general, soft and fungous-like. It varies greatly in thick- 

 ness, and its tenacity is moderate. The mucous membrane 

 is quickly changed by putrefaction, and the sub-mucous tissue 

 still more so, for it is then very easily detached. Whether 

 it is susceptible of being converted into leather by the action 

 of tanning, is not known. 



275. Its force of formation is highly developed; when de- 

 stroyed, it is soon reproduced with all the characteristics of 

 the natural tissue. It is slightly irritable and possesses a 

 higher degree of tonic contractility than the cellular tissue. 

 Its sensibility is vague and obscure throughout the greater 

 part of its extent. Even when inflamed it does not, general- 

 ly, occasion much pain. It is very sensible at the natural 

 openings; and at the entrance of the alimentary and perspira- 

 tory canals, it is the seat of a special sensibility. 



276. Its organic actions or functions are: 



1st. Absorption, which is very active and general, and of 

 which the villi are the most active, but not the only, agents. 



2d. Secretion, which is perspiratory and follicular, and 

 whose products, differing according to the parts, are all, how- 

 ever, known by the name of mucosities. 



3d. Movements of tonic contraction, strengthened in many 

 places by the action of the elastic tissue and even by that 

 of the muscular fibres, with which, in many parts, this mem- 

 brane is surrounded. 



