ORGANS OF SENSE. 149 



continuous with the nail a little beyond its root and lateral borders, and is 

 also continued from the back of the pulpy end of the finger to its concave 

 surface near the end or free edge ; as the nail is thus continuous with the 

 cuticle, so is the matrix with the adjoining cutis. The nails not only protect 

 the sensitive ends of the fingers, but aid them as instruments of prehension, 

 as well as in various manual operations ; they also afford a firm point of 

 support behind the tactile papillae, which is of essential service in the exer- 

 cise of touch. 



4. The Hairs. These cutaneous appendages, like the epidermis and nails, 

 are insensible and non-vascular ; they exist in all parts of the body except 

 the palms of the hand and soles of the feet, varying very much in strength, 

 form, color, and extent, in different situations. On the greater portion of 

 the body, they are short, soft, and downy ; on the head, in the eyelids, 

 axilla, and on the pubic region, they are much longer and stronger ; the 

 extent, however, of their development varies with the age, sex, and tempera- 

 ment of the individual. The loose or projecting portion of a hair is called 

 the shaft ; the 7-oot is fixed in a follicle composed of an involution of the 

 cuticle and of the superficial lamina of the cutis ; this follicle is depressed 

 through the cutis, enlarges into a pyramidal or bulbous form, and is 

 imbedded in the areolar or adipose tissue, from which it receives its vessels, 

 and in which it is so firmly implanted as not to be disturbed by pulling out 

 the hair. The whole follicle is lined by the involuted skin, and at the 

 bottom the cutis presents a highly vascular papilla or pulp, which secretes 

 the matter of the hair. Thus the vessels of the pulp give out the lymph 

 containing cell germs ; these become cells with nuclei, and are gradually 

 condensed and elongated into a scaly fibrous substance which is continually 

 pushed forwards by additions from beneath, and escapes through the open- 

 ing in the epidermis, generally in a slanting manner. The cells forming 

 this outer surface or cortex of the hair are flat and hard, and inclose a 

 more loose fibrous texture named the medulla or pith ; these external scales 

 are successively produced, the last formed overlapping the preceding. 

 Owing to the less density of tha internal cells, the hair when magnified has 

 a cellulo-tubular appearance. Thus the hair is nothing but cuticle specially 

 modified by the papilla on the cutis vera at the bottom of the follicle. Pig- 

 ment granules are also intermingled with and adherent to the cells at th(^ 

 root of each hair ; on these the color of the hair depends. Into the hair 

 follicle one or more sebaceous ducts open, the secretion of which lubricates 

 the hair and imparts to it its oily character. 



5. The Subcutaneous Cellular Tissue is a soft, extensile substratum 

 of the skin, composed of contractile fibres and plates of cellular membrane. 

 It serves to connect the skin with the subjacent fascia, and to conduct ves- 

 sels and nerves to the true skin ; it incloses angular cavities or spaces inter- 

 communicating freely, and filled during life with a watery exhalation. 



6. The Adipose Tissue at one time was supposed to be identical with 

 cellular. It is, however, characterized by consisting of numerous short sacs 

 having no opening or communication, each sac being a delicate simple 

 membrane, supplied with blood-vessels and secreting from its cavit}- the 



855 



