Chap. V.] 



GENERAL HISTOLOGY. 



through the epidermis (out of focus in 30, i.) are large flask- 

 shaped cutaneous glands lined with oblong nucleated cells, which 

 secrete a fluid by which the skin is kept moist, 

 (especially in the toad) is extremely bitter. 



FIG. 30. THE SKIX : HAIRS. 



i. 8km of frog. ii. Skin of human arm. 1, 2, 3. Layers of epidermis, iii. 

 Skin of human thumb, iv. Hair follicle (negro), v. Sebaceous gland 

 (human), vi. External view, white hair of rabbit, vii. Darker hair of rabbit 

 in optical section. 



Fig. 30, ii. and iii. show sections of the human skin of the 

 arm (ii.) and of the thumb (iii.). They show the three layers of 

 the epidermis : (1) An outer layer of non-nucleated horny scales ; 

 (2) a more transparent middle layer, in which nuclei can be 

 seen ; (3) an inner darker layer of distinct and nucleated cells. 

 It is by the constant multiplication of these lower cells that the 

 overlying cells become thrust upwards towards the surface, 

 becoming first flattened and then eventually mere horny scales, 

 which are continually being shed. 



Beneath the epidermis is the dermis. This is raised into 

 papillce, to which the epidermis is moulded, and in the papilla) 

 of the thumb the tactile corpuscles may be readily seen under a 

 high power. Deeper in the dermis lie the large oval pacliuaii 



