CLASSIFICATION OF ANIMAL PEEPAEATIONS. 439 



the prismatic, and the spheroidal ; of these, the last two kinds 

 are sometimes provided with vibratile ciha; the latter, or 

 under surface, is supported upon a submucous areolar tissue, 

 in which both the blood-vessels and nerves ramify, but do not 

 in any case enter the mucous membrane. Of all the valuable 

 discoveries made by the microscope in minute anatomy, none 

 can equal in importance that by which a true knowledge 

 of the structure of the mucous membranes has been obtained, 

 for these very important results we are mainly indebted to the 

 labours of Henle and Bowman; the latter gentleman has 

 divided them into two parts, viz., the basement membrane and 

 epithelium ; the name of hasement membrane has been given 

 to the tissue upon which the epithelium rests, and which 

 forms the basis of the strength and cohesive power that 

 mucous membrane possesses ; in itself it is structureless, but 

 of various degrees of thickness in different parts, and either 

 it or the epithelium is always present where mucous mem- 

 brane may be said to exist. When the skin is compared 

 accurately with mucous tissue, they will both be found to be 

 parts of one expanded membrane, with certain modifications, 

 according to the office which each is destined to perform ; the 

 epithelium of skin is the cuticle or epidermis, but the base- 

 ment membrane, though present, is not easily shown, except 

 where the surface is raised into papillae. The mucous 

 membrane, and its three kinds of epithelium, form by far the 

 largest proportion of the preparations wliich the anatomist 

 will find necessary to examine, and the same, when its 

 capillary system is injected, becomes one of the most beautiful 

 of any of the classes of microscopic objects. 



The Epithelium, as has been already stated, consists of three 

 varieties, viz., the scaly, the prismatic, and the spheroidal. 

 The first kind is seen most largely developed in the skin, 

 where it forms the cuticular layer ; detached scales maybe 

 obtained from the inner side of the mouth, or viewed in 

 situ on the transparent web of the frog's foot ; and the entire 

 structure of horns, hairs, hoofs, feathers, and other cuticular 

 appendages is made up of it. The prismatic, or, according 

 to Dr. Todd, the columnar, is abundant throughout the 



