244 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



with epithelium-cells, which, being filled with fatty matter, resemble the cells 

 of adipose tissue ; the number of these sacculi generally varies from four or five 

 to twenty, but in rare cases it is reduced to three, two, or even one. The size 

 of these glandulae, and the number which open into the same hair-follicle, bear 

 no proportion to the size of the hair; but are rather related to the necessity 

 which may exist, on the several parts of the surface, for their lubrifying secre- 

 tion. Some of the largest of them are found in connection with the fine downy 

 hairs of the nose and of other parts of the face; and their orifices being often 

 obstructed by particles of foreign matter, they become distended with their adi- 

 pose secretion, and not unfrequently afford the nidus to a curious parasite, which 

 seems to belong to the Arachnidan class, and is not known to exist elsewhere. 1 

 The development of the Sebaceous glandulae, which has been recently made 

 the subject of careful study by Prof. Kolliker, 2 commences at about the sixth 

 month of foetal life, in a sort of excrescence of the cellular lining (root-sheath) 

 of the hair-follicle (Fig. 34, A, d) t which is, in fact, a continuation of the 



Fig. 34. 



Development of the Sebaceous Glands, in connection with the hair-follicle?, from a Foetus of six months ; 

 A, incipient development of the glandular papilla, from the cells of the outer root-sheath ; B, the same, hav- 

 ing assumed the flask-shape, and showing the first appearance of fat-cells in its interior ; c, extension of the 

 formation of fat-cells through the pedicle, and their expulsion into the hair-canal ; a, hair ; ft, inner root- 

 sheath ; c, outer root-sheath ; d, incipient sebaceous glands. 



deeper portion of the Epidermis ( 241). Each of these little processes, which 

 is at first solid, soon assumes somewhat of a flask-shape, through the narrowing 

 of its neck (B, d) ; but as its development advances, a group of cells containing 

 fat-particles appears in its centre, and gradually extends itself along the axis of 

 the pedicle, until it penetrates through the root-sheath (c); and the fat-cells thus 

 escape into the cavity of the hair-follicle, and constitute the first secretion of 

 the sebaceous gland. They are soon succeeded by others of the same kind, and 

 the little gland is established in its office ; additional sacculi and recesses being 

 subsequently formed by the budding-out of its cellular lining, as the first was 

 produced by out-growth from the root-sheath. The purpose of the Sebaceous 

 secretion is to keep the Skin from being dried and cracked by the action of heat 

 and of air, and thus to maintain its flexibility; and also to diminish the friction 

 between those parts of the surface which move one over another. Hence we 

 find it especially abundant on the integument of the face and head, which is 

 necessarily more exposed than that of any other part to the sun and atmosphere; 



1 See Dr. Gustav. Simon, in " Muller's Archiv.," 1842; Mr. Erasmus Wilson, in "Philos. 

 Transact.," 1844, and "Healthy Skin," 3d edit. pp. 50-53; and Prof. Owen's "Lectures 

 on Comparative Anatomy," vol. i. p. 252. 



2 " Mikroskopische Anatomic," band ii. pp. 192-196. 



