DEVELOPMENT OF THE SKIN AND ITS APPENDAGES. gate) 
follicle, whilst the deeper cells undergo proliferation. The size of the gland bears 
no proportion to that of the hairs, since they are very large in the minute hair 
follicles of the foetus and newly born child, and also in the follicles of the rudimen- 
tary hairs of the nose and certain parts of the face. 
Bundles of non-striped muscular fibre are associated with the hair follicles, and 
are named the mm. arrectores pilorum. Attached to the deep part of the hair follicle, 
and forming with it an acute angle, they pass outwards close to the sebaceous 
glands, to end in the papillary layer of the corium. Situated on the side of the 
hair towards which it slopes, they, on contraction, diminish the obliquity of 
the hair follicle and render the hair more erect, and, at the same time, com- 
press the sebaceous glands and expel their contents. The condition of “ goose- 
skin” is caused by the contraction of these slender muscles. 
Thomson suggests that the condition of curly hair is produced by the contraction of these 
small muscles. Straight hair is thick and rounded ; curly hair is flat and ribbon-lke. When 
the erector muscle contracts, the thick rounded hair resists the tendency of the muscle to bend it, 
while the flat hair, not sufficiently strong to resist the strain of the muscle, becomes bent, and 
this is probably the explanation why the follicle assumes the curved form characteristic of the 
scalp of a bushman. The sebaceous gland lies in the concavity of the bend between the follicle 
and the muscle, and forms a mass of greater resistance, around which the follicle may be curved 
by the contraction of the muscle. The cells at the root of the hair accommodate themselves to 
the curved follicle, and, becoming more horny as they advance to the surface, retain the form 
of the follicle in which they are moulded. 
The sudoriparous or sweat glands (glandul sudorifere) are relatively few in 
number on the back of the trunk, but are very plentiful on the palms and soles, 
where they open on the summits of the curved ridges. Each consists of an elongated 
tube, the deeper portion of which forms its secretory part and is coiled in the sub- 
cutaneous tissue or deep part of the corium in the form of an ovoid or spherical ball, 
termed the glomerulus or corpus glandule sudorifere (Fig. 536). The superficial part 
of the tube, or ductus sudoriferus, extends through the corium and epidermis, in 
which it is spirally coiled, if the epidermis be thick, and opens on the surface by a 
funnel-shaped orifice, the porus sudoriferus. The glomeruli, as a rule, vary in 
diameter from 0-1 to 0°5 mm., but in the axille they are much larger and may, 
measure 1-4 mm. Each is surrounded by a capillary network and by a capsule of 
connective tissue, inside which is a homogeneous basement membrane. The lumen 
of the tube is lined by a layer of nucleated, granular, and striated, columnar, or 
prismatic epithelium, between the deep extremities of which and the basement 
membrane is a layer of non-striped muscular fibres, the long axis of which is more 
or less parallel to the long axis of the tube. The excretory ducts are devoid of 
muscular fibres, and consist of a basement membrane lined by two or three layers 
of polyhedral cells, which are covered, next the lumen of the tube, by a thin 
cuticle. 
The glands of Moll (glandulz ciliares), opening at the margins of the eyelids, and 
the glandule ceruminose of the external auditory meatus, are modified sudoriparous 
glands; the former are, however, not coiled up to form glomeruli, while the cell 
protoplasm of the latter contains yellowish pigment, and their gland ducts, in the 
foetus, open into hair follicles. 
DEVELOPMENT OF THE SKIN AND ITS APPENDAGES. 
Skin.—The vascular and sensitive corium is developed from the mesoblast, the cells 
of which, immediately underlying the epiblast, have, by the second month of foetal life, 
become aggregated together and flattened parallel to the surface of the embryo. By the 
third month they are seen to form two layers, the superficial of which becomes the 
corium, and the deeper the subcutaneous tissue. The epidermis, nails, hairs, sweat and 
sebaceous glands are all of epiblastic origin. 
The epidermis at first consists of a single layer of cells, but by the end of the second 
month it is duplicated, and then exhibits a superficial layer of irregular and a deeper layer 
of more cubical cells. By the third month three strata are seen: (@) a deep layer, con- 
sisting of a single stratum of cubical cells—the future stratum germinativum ; (4) a 
middle layer, comprising two or three strata of irregular cells—the future stratum 
mucosum ; and (c) an outer layer, a double stratum of large cells. This outer layer 
