1062 ORGANS OF THE SENSES AND THE COMMON INTEGUMENT 





one to three or four in number; entering the fibrous capsule, they divide several times, and, 

 losing their medullary sheaths, ultimately end in naked axis-cylinders encircling the intrafusal 

 fibers by flattened expansions, or irregular ovoid or rounded disks (Fig. 939). Neuromuscular 

 spindles have not yet been demonstrated in the tongue muscles, and only a few exist in tho 

 ocular muscles. ^Hl 



FIG. 939. Middle third of a terminal plaque in the muscle spindle of an adult cat. (After Ruffini.) 



THE COMMON INTEGUMENT (INTEGUMENTUM COMMUNE; SKIN). 



The integument (Fig. 940) covers the body and protects the deeper tissues from 

 injury, from drying and from invasion by foreign organisms; it contains the per- 

 ipheral endings of many of the sensory nerves; it plays an important part in the 

 regulation of the body temperature, and has also limited excretory and absorbing 

 powers. It consists principally of a layer of vascular connective tissue, named the 

 corium or cutis vera, and an external covering of epithelium, termed the epidermis 

 or cuticle. On the surface of the former layer are sensitive and vascular papillae' 

 within, or beneath it, are certain organs with special functions : namely, the sudorif- 

 erous and sebaceous glands, and the hair follicles. 



The epidermis, cuticle, or scarf skin is non-vascular, and consists of stratified 

 epithelium (Fig. 941), and is accurately moulded on the papillary layer of the corium' 

 It varies in thickness in different parts. In some situations, as in the palms of the 

 hands and soles of the feet, it is thick, hard, and horny in texture. This may be in 

 a measure due to the fact that these parts are exposed to intermittent pressure, 

 but that this is not the only cause is proved by the fact that the condition exists 

 to a very considerable extent at birth. The more superficial layers of cells, called 

 the horny layer (stratum corneum), may be separated by maceration from a deeper 

 stratum, which is called the stratum mucosum, and which consists of several layers 

 of differently shaped cells. The free surface of the epidermis is marked by a 

 net-work of linear furrows of variable size, dividing the surface into a number of 

 polygonal or lozenge-shaped areas. Some of these furrows are large, as opposite the 

 flexures of the joints, and correspond to the folds in the corium produced by move- 

 ments. In other situations, as upon the back of the hand, they are exceedingly 

 fine, and intersect one another at various angles. Upon the palmar surfaces of the 

 hands and fingers, and upon the soles of the feet, the epidermal ridges are very dis- 

 tinct, and are disposed in curves; they depend upon the large size and peculiar 

 arrangements of the papillae upon which the epidermis is placed. The function 

 of these ridges is primarily to increase resistance between contact surfaces for the 

 purpose of preventing slipping whether in walking or prehension. The direction 

 of the ridges is at right angles with the force that tends to produce slipping or to 

 the resultant of such forces when these forces vary in direction. 1 In each individual 



1 Whipple, Inez L., The Ventral Surface of the Mammalian Chiridium, etc., Zeit. f. Morph. u. Anthropol.- 

 1904, vol. vii. 



