16 OUTLINES OF EqUINE ANATOMY. 



membranes that we find it gaining its greatest complexity, 

 in some cases consisting of several superimposed layers, the 

 most internal of which, drawing nutriment from the blood, 

 ''hands it on" to those more externally placed. This is 

 stratified epithelium. In some cases, however, as in the 

 guttural pouch, we find the mucous membrane resembling 

 a serous membrane in the simplicity of its component 

 elements. The vascular layer of mucous membrane is 

 termed corium, and is sometimes thick, presenting numerous 

 and large blood-vessels, as in the case of the mucous mem- 

 . brane of the hard palate. In some situations it is extremely 

 attenuated or even, as in the corneal conjuctiva, completely 

 absent. Epithelium of mucous membrane is of two kinds, 

 ciliated or non-ciliated. Non-ciliated epithelium may be 

 either tessellated (above described) or, the mutual compres- 

 sion of the cells not being so great, they may retain the 

 spheroidal figure (as in the bladder, ureters, and pelvis of 

 the kidney) , or the cells may be cylindrical, fitting in closely 

 together, having one extremity free, the other in contact 

 with the basement membrane. This is columnar epithe- 

 lium ; it lines the greater portion of the digestive tract. 

 Either columnar or spheroidal cells may present on their 

 free surface a number of small pointed prolongations 

 which, by some peculiar power independent of nerve in- 

 fluence, wave to and fro. These are ciliae, their presence 

 is manifest in the respiratory tract, where their action serves 

 to waft upwards mucus for expectoratiou ; and also in the 

 Fallopian tube, where they waft the sperm- cell upwards, 

 the germ-cell downwards. Mucous membrane lines all 

 those great cavities of the body which communicate with the 

 external air, but the distinction hetween the mucous and serous 

 membranes is very artificial. Thus, the alimentary, respira- 

 tory, genito-uriimry and lachrymal tracts are all lined by 

 mucous membrane, and as this insensibly blends with the 

 skin at the external openings of the body, we may look 

 upon the structures of the body already described as con- 

 tained in a large sac of compound membrane. In some 

 parts the corium of mucous membranes presents unstriated 

 muscular fibre, in others it is thickened at certain points 

 producing papillce, such as those found on the tongue 

 and the intestinal mucous membrane. Other peculiarities 

 in the mucous membranes will be noticed in the descrip- 

 tions of different parts ; thus, the teeth, as will be shown, 



