496 



MUCOUS MEMBRANE. 



lying underneath it; and am come to the con- 

 clusion that the most complicated diversities 

 that are met with, admit, when studied in this 

 manner, of being explained and reconciled to 

 a common type of structure. 



Peculiarities of the skin, mucous membranes, 

 and glands. 



Of the skin. This is chiefly peculiar in its 

 epithelial element and its submucous areolar 

 tissue. The epidermis is composed of a vast 

 number of superimposed laminae of scales, 

 which, in the earlier stages of their develope- 

 ment, and especially in certain races of man- 

 kind, contain minute pigment granules in their 

 interior. The pigment disappears more or less 

 completely as the particles attain the surface. 

 It is continued for some distance down the hair 

 follicles and sweat-ducts, and thus serves to mark 

 the continuity of these parts with the general 

 surface. Hairs, nails, hoofs, and other simi- 

 lar appendages are all composed of modified 

 epithelial particles, and are nearly peculiar to 

 the skin. Tiie sebaceous and perspiratory 

 glands, and the spiral ducts of the latter travers- 

 ing the epidermis, are also among the most 

 characteristic features of this part of the mucous 

 system. The papillae of the skin have their 

 counterpart in the villi of the mucous mem- 

 branes ; the cutis vera, as it is called, has also 

 its analogue in the submucous areolar tissue, 

 but it is so enormously developed that the re- 

 semblance has escaped the notice of anatomists. 

 Its characters have been already briefly de- 

 scribed. It is a striking fact that the cutis, like 

 the submucous areolar tissue, contains no fat, 

 even in the most corpulent subjects. I have 

 repeatedly made this remark. The cutis differs 

 in this respect from the subcutaneous fascia, 

 which is therefore, perhaps, to be regarded as 

 less allied to the submucous areolar tissue. 



Of the mucous membranes These hold an 

 intermediate place between the skin and the 

 true glands. They blend insensibly with the 

 former at the different orifices of the body, and 

 may, under favourable conditions, become so 

 modified as to assume the appearance of skin. 

 The change then wrought is nothing more, 

 however, than an increased deposit of epithelial 

 scales, with an absence of the natural moisture; 

 and it may be doubted whether a transforma- 

 tion of this kind could occur in a mucous 

 membrane of which the epithelium was not of 

 the scaly variety. On the other hand certain 

 parts of the membranes usually termed mu- 

 cous are nothing less than real glands arranged 

 in a membranous form. 



The mouth, pharynx, oesophagus, the vagina 

 and vaginal surface of the uterus, are the parts 

 whose lining membrane most nearly resembles 

 the skin. Their most remarkable feature is the 

 thickness of their covering of epithelial scales, 

 provided for their protection against foreign 

 contact and pressure, and in connection with 

 this the existence of numerous glands opening 

 upon them for the lubrication of their surface. 

 Many of these glands correspond with the 

 sweat-glands of the skin in being similarly 

 scattered under the surface. Such are the 



buccal and all the small glands allied to them, 

 which, in particular, resemble the largely deve- 

 loped sweat-glands of the axilla. The only 

 difference between them is in the mode of in- 

 volution of the secreting membrane, which in 

 the former is cellulated, in the latter tubular. 

 These portions of the mucous membranes also 

 approach the skin by the denseness of their 

 submucous areolar tissue. 



In the pharynx it is only that part of the 

 lining membrane below the posterior arches of 

 the palate, or that exposed to friction during 

 deglutition, that has the dermoid characters 

 now described : all above is more delicate, is 

 clothed with ciliated epithelial prisms, and be- 

 longs physiologically to the nasal or respiratory 

 tract. The lower or buccal surface of the soft 

 palate differs in a similar way from the upper. 



The lining membrane of the Eustachian 

 tubes and tympana is very delicate, none of 

 the elementary tissues predominating. The 

 epithelium is in a single layer of prisms clothed 

 with cilia. The submucous areolar tissue is in 

 very small quantity, and the vascular network 

 consists of little more than a simple plane ex- 

 pansion. In the nose, the epithelium, accord- 

 ing to Henle, is scaly on the septum and on 

 the alae for some way within the nostrils. Here 

 also there are hairs an advance towards the 

 characters of the skin ; beyond this it is every- 

 where ciliated, even within the bony sinuses. 

 The membrane covering these sinuses is of 

 extreme tenuity, and presents the elementary 

 tissues all in a simple form. That covering the 

 pendulous parts of the spongy bones, on the 

 contrary, has long been noted for its great 

 thickness a character due to neither of the 

 elements of the mucous tissue itself, but to the 

 extraordinary size of the submucous vessels. 

 Both arteries and veins are large, but especially 

 the latter, which here form a plexus imme- 

 diately beneath the surface, and not separated 

 from it by any considerable quantity of dense 

 areolar tissue. Hence the facility with which 

 these vessels give way externally when dis- 

 tended with blood. The lining of the nose 

 has been sometimes called ajibro-mucous mem- 

 brane, from its close connection with the pe- 

 riosteum. The periosteum in the sinuses is 

 extremely delicate, in consequence of the te- 

 nuity of the bony laminae it invests; and it 

 would perhaps be impossible to separate it 

 there from the submucous areolar tissue. The 

 globe and cornea are covered with scaly epithe- 

 lium, of which the particles are smaller towards 

 the folds of the eyelids,* where they gradually 

 become prismatic, and along the tarsal borders 

 clothed with cilia, so small as to be only recog- 

 nizable a short time after death. The conjunc- 

 tiva of the lower lid is very minutely villous. 

 At the pharyngeal orifice of the glottis, the 

 epithelium becomes ciliated and continues so 

 along the trachea and bronchial ramifications 

 as far as the air-cells, but, according to my 

 own observations, the cilia there cease, and the 

 epithelium changes its character to a remark- 

 able variety of the glandular form. In the air- 



* Henle, loc. cit. 



