1290 THE SKIN, MAMMARY GLANDS AND DUCTLESS GLANDS 



and their areas of distribution will be found described in detail in the section on the Nervous 

 System. 



With the exception of the nerves to the sudoriferous and sebaceous glands, the skin-muscles 

 and blood-vessels, all the cutaneous nerves are sensory. They have diverse modes of termina- 

 tion. Some end in the subcutaneous tela; others, the greater number, terminate in the corium; 

 still others extend to the epidermis. 



Toward their termination the nerves branch and rebranch, and just beneath the surface they 

 form a great number of small twigs from which the terminal fibres arise. These may be divided 

 into two groups, those that end freely and those whose termination is surrounded by a capsule. 

 The free ends are slightly enlarged and terminate in the epidermis and in certain regions in the 

 corium. The encapsulated terminations form special end organs and are found in the corium as 

 the bulbous corpuscles (end-bulbs of Krause) [corpuscula bulboidea, KrauseriiJ; the tactile 

 corpuscles (corpuscles of Meissner or Wagner) [corpuscula tactus, Meissneri]; and the genital 

 corpuscles [corpuscula nervorum genitahaj. In the subcutaneous tela the end-bulbs are seen as 

 the lamellous corpuscles (corpuscles of Vater: Pacinian corpuscles), [corpuscula lamellosa; 

 Vateri, Pacini] shown in fig. 1049; the Golgi-Mazzoni corpuscles and the Ruffini corpuscles. 

 All the terminations except the lamellous corpuscles are microscopic, not exceeding 0.2 mm. in 

 length. The lamellous corpuscles, which are readily seen in reflecting the skin from the fingers 

 and toes, maj^ be as much as 2 mm. long and half as thick (fig. 1049). The exact function of 

 each of the various endings is not known. They are undoubtedly sensory fibres except those to 

 the glands, muscles, and blood-vessels. 



Development of the corium and subcutaneous tela.^ — The corium is developed from the 

 superficial part of the myotome or dermo-muscular plate of mesoderm. At first it is very largely 

 cellular but later fibres are produced. In the earlier stages the corium and tela subcutanea are not 

 distinguishable and only in the later embryonic period may the corium be separated into the 

 papillary stratum and the tunica propria. 



THE APPENDAGES OF THE SKIN 



The appendages of the skin include: (A) the hairs; (B) the nails; (C) the 

 cutaneous glands; and (D) the mammary glands. 



A. THE HAIRS 



The hairs [pili] are less developed in man than in any other primate. Where 

 well developed they in themselves serve as a protective organ and moreover 

 through their connection with the nervous system they become in a measure 

 organs of special sense. They are strong, flexible, somewhat elastic, and poor 

 conductors of heat. They cover the entire surface of the body with the following 

 exceptions: The flexor surfaces of the hands and feet; the dorsal bends and sides 

 of the fingers and toes; the dorsal surfaces of the distal phalanges of the fingers 

 and toes; the red borders of the lips; the glands and inner surface of the prepuce 

 of the penis and clitoris; the inner surface of the labia majora; the labia minora 

 and the papilla mammae. 



The size and length of hairs varies greatly not only in different parts of the 

 body but also in different individuals and races. In certain situations the hairs 

 are especially long and large and are designated by special names. 



Thus upon the scalp, capilli, in the axillary region, hirci, and after puberty upon the face in 

 the male, the beard, barba, and in the pubic region in both sexes, pubes. The pubic hairs extend 

 upon the external genital organs and upon the ventral abdominal wall toward the umbilicus. 

 All of the hairs of these regions are not long and large but short and finer hairs are mixed 

 with them in varying numbers. Strong, well-developed short hairs are found in connection with 

 the organs of sense forming the eyebrows, supercilia, the eyelashes, cilia, at the entrance to the 

 external acoustic meatus, tragi, and at the nares, vibrissas. Upon the extensor surfaces of the 

 extremities, upon the chest, and in other situations in some individuals, especially in adult 

 males, the hairs are also longer and stronger than upon the rest of the body, where they are, as a 

 rule, short, fine and down3^ The first hairs appearing in the fcrtus are very fine, and are called 

 lanugo. The long hairs of the adult scalp may attain a length of 150 cm. or more; the short 

 hair.s average from .5 to 1..3 cm. in length, while the lanugo does not exceed 1.4 cm. 



Excess of long hairs, hypertrichosis, may involve the whole hairy surface of the body. It is 

 usually inherited and affects several individuals in the same family. Local areas of long hairs 

 al.so occur as over mv.vi and upon the sacrum. Local congestion due to inflammation, irritation, 

 or pressure may cause hypertrichosis. In women, hair upon the upper lip or other parts of the 

 face may be an inherited peculiarity or due to some abnormality of the sexual organs. It is also 

 not uncommon after the menopause. 



In diameter the hairs vary from .005 mm. for the finest lanugo to .203 mm. 

 for the coarsest hair of the beard; but they usually taper toward the tip and also 

 are narrower toward the base. As a general rule, blonde hairs are the finest and 

 black hairs the coarsest. 



