OF THE HAIRS. 187 



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from those lying between the hair and the outer sheath. The proper 

 hair-sac is formed, in its fibrous layers, essentially in loco, out of the 

 formative cells which surround the rudiment of the hair ; possibly, how- 

 ever, they may be considered as an involution of the cutis, produced by 

 the ingrowing process of the epidermis. Its structureless membrane, 

 which appears very early, is, not improbably, closely related to the ex- 

 ternal cells of the rudiment of the hair, answering to the outer hair- 

 sheath, and formed by an excretion from them like the membrane* pro- 

 price of the glands; as to the papilla, it is hardly possible to consider it 

 as anything but an outgrowth of the fibrous layer of the hair-sac, 

 analogous to the papillae of the cutis in general ; though the circumstance 

 that it appears at a time when the hair-sac is hardly demonstrable as a 

 whole, and that it may always be pulled out together with the rudiments 

 of the hair and root-sheath, is apparently opposed to this view. 



The first rudiments of the downy hairs and of their sheaths, are found 

 in the human embryo at the end of the third or at the beginning of the 

 fourth month, upon the forehead and eyebrows. They consist of papilli- 

 form masses of cells 0-02 of a line in diameter (Fig. 73) which are 

 visible, even to the naked eye, as minute whitish spots separated by 

 regular intervals. They are continuously connected with the rete Mal- 

 pighii of the epidermis, and are nothing more than perfectly solid pro- 

 cesses of it, which penetrate obliquely Fig. 73. 

 into the corium, and here lie in the 

 meshes of a delicate capillary network. 

 These cells are spherical, 0-003-0-004 

 of a line in diameter, and consist of a 

 clear granular substance and round 

 nuclei of 0-002-0-003 of a line. 

 Nothing was to be seen of any dermic "* 

 investment of these rudiments ; in other words, the foundation of what 

 I have described as the proper hair-sac was not laid. In the fifteenth 

 week the processes were already larger (0-025-0-03 of a line long, 

 0-013-0-02 of a line broad), flask-shaped, and surrounded by a thin 

 structureless investment, which was continued into a delicate membrane 

 lying between the cutis and the rete Malpighii, but united more closely 

 with the latter. Besides this investment, which is, probably, only the 

 structureless membrane which I have discovered in the perfect hair (see 

 60), another external layer of cells occurs on the hair-sacs, which can 



FIG. 73. Rudiment of the hair from the brow of a human embryo, sixteen weeks old; 

 iun;:iiified 350 diameters: a, horny layer of the epidermis ; 6, its mucous layer; t, structure- 

 less membrane surrounding the rudiment of the hair and continued between the mucous 

 layer and the corium ; m, roundish, partly-elongated cells, which especially compose the 

 rudiment of the hair. 



