496 
lying underneath it; and am come to the con- 
clusion that the must 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 lamine 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. The 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 papille 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, uuder 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, wsophagus, 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. 
any of these glands correspond with the 
sweat-glands of the skin in being similarly 
scattered under the surface. Such are the 
MUCOUS MEMBRANE. 
buccal and all the small glands allied to them, 
which, in particular, resemble the ly deve- 
loped sweat-glands of the axilla. e only 
difference between them is in the mode of in- 
volution of the secreting membrane, which 
the former is cellulated, in the latter tubular. 
These portions of the mucous membranes a! 
a tm the skin by the denseness of th 
submucous areolar tissue. ‘w 
In the pharynx it is only that part of th 
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 respirator 
tract. e 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 i ne 
ao 
* 
redominating. Th 
epithelium is in a single layer of prisms clothed 
with cilia. The submucous areolar tissue is it 
very small quantity, and the vascular network 
consists of little more than a simple plane ex 
pansion. In the nose, the epithelium, accor 
ing to Henle, is scaly on the septum and ot 
the ale for some way within the nostrils. Here 
also there are hairs—an advance towards th 
characters of the skin; beyond this it is every- 
where ciliated, even within the bony sinuses 
The membrane covering these sinuses is ¢ 
extreme tenuity, and presents the elementat 
tissues all in a simple . That covering th 
pendulous parts of the spongy bones, on thi 
contrary, as long been noted for its gre 
thickness—a character due to neither of 
elements of the mucous tissue itself, but to # 
extraordinary size of the submucous sels 
Both arteries and veins are large, but especial 
the latter, which here form a plexus imme 
diately beneath the surface, and not separat 
from it by any considerable quantity of dens 
areolar tissue. Hence the facility with wh 
these vessels give ite Baier when 
tended with blood. The lining of the no 
has been sometimes called a fibro-mucous me 
brane, from its close connection with the } 
riosteum. The periosteum in the sinuses 
extremely delicate, in consequence of the 
nuity of the bony lamine it invests; a 
would perhaps be impossible to separat 
there from the submucous areolar tissue. “ 
globe and cornea are covered with scaly 
lium, of which the particles are smaller tow 
the folds of the eyelids,* where they gradu 
become prismatic, and along the tarsal bor 
clothed with cilia, so small as to be only rt 
nizable a short time after death. The conji 
tiva of the lower lid is very minutely vil 
At the pharyngeal orifice of the glottis, 
epithelium becomes ciliated and contin 
along the trachea and bronchial ramifiea 
as far as the air-cells, but, according to 
own observations, the cilia there cease, and 
epithelium changes its character to a rem 
able.variety of the glandular form. In the 
* Henle, loc. cit. 
