EPIDERM OF MAMMALS. 



613 



The wing-membrane is sometimes further developed, so as to 

 be disposed at one part in the form of a pouch, as in the genus of 

 Bat thence called Saccopteryx, in which the pouch is plicated, 

 and its linear orifice is near the head of the humerus. The 

 delicate organisation, of these modifications of the derm has been 



o 



noted at p. 189 ; and, as regards its vascular structure, at pp. 549 

 and 553. The conchal or auricular productions of the derm are 

 considerable in all Bats : the two outer ears are confluent, or united 

 by a transverse fold of skin, crossing the forehead, in Nycteris 

 and Megaderma ; in these and many other genera, e.g. Rhino- 

 po?na, Rhinolophus, Phyllostoma, the nose, also, is furnished with 

 a crest or with foliaceous lamellae. 



The sudoriferous or sweat-glands, fig. 486, i, consist of a fine 

 secerning tubule, cjiled up into a ball, and situated at the under 

 surface of the derm or in the subcutaneous 

 tissue, k : the duct traverses the derm, at first 

 in a wavy course, y, becoming straighter in the 

 denser peripheral part, and spiral as it passes 

 through the epiderm, b, to terminate at the 

 sweat-pore. The sebaceous glands relate chiefly 

 to the hairs, and mostly open into the hair- 

 sheath or follicle, fig. 487, h. The movements 

 of the derm are due either to intrinsic or ex- 

 trinsic muscles : the former, ib. g, which are 

 smooth as a rule, produce the shrinking called 

 6 cutis anserina,' on account of the protrusion 

 of the hair-sheaths, and the depression of the 

 intervening part of the skin ; the extrinsic 

 muscles, which have striped fibres, move more 



or less of the integument, as when cattle after 



~ 



a shower, or a dog quitting the water, shake 



off the moisture, or when a fly or other irritant is sought to be 



dislodged. 



~ 



358. Epiderm. Upon the papillose surface of the derm, in 

 the embryo, albuminoid atoms in the solution exuding therefrom 

 formify as cells, and between the outermost of these, condensed 

 and dried by exposure after birth, and the derm, formifaction con- 

 tinues, throughout life, to produce a precipitate of cells. These, at 

 first, are perpendicular to the derm, in one or more strata ; then, as 

 they are pushed off by newly formed cells, they assume a more 

 rounded shape, lose their soft granular contents, afterwards their 



Section of Uumau skin, 

 inaarii. 1 



1 The derm,/, so magnified, i.s considerably thicker than here represented. 



