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PRODUCTS OF THE EPIBLAST AND MESOBLAST. 561 ;

of small polyhedral granular cells containing oval nuclei ; this is the
continuation of the infant layer of rete Malpighii. Very frequently
these cells are seen to contain droplets of oil. Their office is to secrete
the oil which serves to lubricate the hair and skin. Inside this layer,
Fig. 307.

Sebaceous Gland and Hair: 1, hair-follicle; 2, simple gland; 0, 4, 5, compound glands.
and occupying the cavity of the gland, are seen cells which have been
pushed off from the outer layer, and which become larger as they near
the central portion of the gland. The older cells pass through varying
stages of fatty degeneration until they are forced from the mouth of
the gland as sebum, a substance holding in suspension minute oil-glob-
ule-^. The sebaceous glands rest upon the erector papillre muscles,
and are moved as the hairs move. No doubt the action of these
muscles materially aids the ejection of the contents of the glands
vigorous brushing of the hair tends to increase the flow of this oily
secretion.
Siveat- Glands.—The other glands developed from the epithelium are
the tubular sweat-glands. Their development does not differ materially
from that of the sebaceous glands, except that instead of assuming a race-
mous form they curl or coil upon themselves at their deepest extremity,
in a very peculiar manner, presenting the appearance of a ball (Fig. 308).
Vol. I.—36