856 



THE SKIN OK INTEGUMENT. 



hair-like extremities of the gustatory cells, and so renders them ready to be 

 stimulated by successive substances. It should be added that there is a close 

 association between the senses of smell and taste. This can be best appreciated by 

 considering the defective taste perceptions resulting from inflammatory conditions 

 of the nasal mucous membrane, or the common practice of holding the nose in 

 order to minimise the taste of nauseous drugs. 



The development of the tongue is described on pp. 45-46. 



INTEGUMENTUM COMMUNE. 



Duct of 

 sweat gland 



Ha 



Hair follicle 



Glomerulus 



of sweat 



gland 



The integument or skin covers the body, and is continuous, at the orifices on 

 its surface, with the mucous lining of its alimentary and other canals. It contains 

 the peripheral terminations of many of the sensory nerves, and serves as an organ 

 of protection to the deeper tissues. It is the chief factor in the regulation of the 

 body temperature, and by means of the sudoriferous and sebaceous glands, which 



open on its free 

 surface, consti- 

 tutes an important 

 excretory struc- 

 ture. Its super- 

 ficial layers are 

 modified to form 

 appendages in the 

 shape of hairs and 

 nails. 



The skin is 

 very elastic and 

 resistant, and its 

 colour, determined 

 partly by its own 

 pigment and 

 partly by that of 

 the blood, is deeper 

 on exposed parts 

 and in the regions 

 of the genitals, 

 axillae, and mam- 

 mary areolse, than 

 elsewhere. The 

 colour varies also 

 with race and age, 

 the different races 

 of the world being 

 roughly classified, 

 according to the 

 colour of their 

 skin, into the 



three groups of white, yellow, and black. Pinkish in colour in childhood, the skin 

 assumes a yellowish tinge in old age, while in certain diseases (e.g. icterus and 

 melasma Addisonii) the colour undergoes marked alteration. 



The surface of the skin is perforated by the hair follicles and by the ducts of the 

 sudoriferous and sebaceous glands, and on the palms, soles, and flexor aspect of the 

 digits it presents numerous permanent ridges, the cristse cutis, which correspond 

 with rows of underlying papillae. Over the terminal phalanges these ridges form 

 distinctive patterns, which are retained from youth to old age, and are utilised for 

 purposes of identification. Ketinacula of the skin are seen in the neighbourhood 



Papilla of hair 

 FIG. 733. VERTICAL SECTION OF THE SKIN (schematic). 



Oblique section through 

 a Pacinian corpuscle 



