OEGANS OF THE BODY. 605 



closer meshes. The lymphatics of the cutis vera do not contain valves, 

 which first appear in the subcutaneous areolar tissue. 



The arrangement of these vessels varies much in the different localities. 

 Here and there blind-ended offshoots of varying thickness are met with. 

 In the papillae of the skin the lymphatics present sometimes single tubes, 

 sometimes loops. 



The several complementary structures of the skin, as the hairs with 

 their sebaceous follicles and the sweat glands, all possess their own special 

 lymphatic vessels; even the fat lobules are surrounded with looped 

 canals. The lymphatic vessels are very highly developed in the sub- 

 cutaneous areolar tissue. 



The various parts of the body present considerable difference as to the 

 number of these vessels to be found. The parts which seem to be most 

 richly supplied with them are the scrotum, labia majora, palms of the 

 hands, and soles of the feet. 



The arrangement of the nerves of the skin in plexuses, which constitute 

 the latter one of the apparatuses of special sense, has been before touched 

 on in the second part of our work. We refer to 185 and 187 for a 

 description of the several modes of termination of the nerves, in the 

 first place in the tactile corpuscles, and then at other points. In 184 

 the scattered observations on the occurrence of the end bulbs of Krause 

 are mentioned. 



The development of the epidermis in the embryo has been already 

 treated of at p. 159. The cutis still consists entirely, according to Koel- 

 liker, in the fourth and fifth month of human intra-uterine life, of collec- 

 tions of round and fusiform formative cells, and has a thickness of 

 O'Ol 35-0*0226 mm. In the third month the subcutaneous areolar tissue 

 may be distinguished, and both layers are of about the same depth. 

 Both together, including the cuticle, measure (H353 mm. A month 

 later the first lobules of fat may be remarked, and in the sixth month the 

 papillae make their appearance, the corium having attained a thickness 

 of 1*13 mm. and upwards. In the new-born infant the panniculus 

 adiposus is particularly strongly developed. 



302. 



The glandular structures which lend to the skin the character of a 

 secretory organ are of two kinds, perspiratory and sebaceous. 



The sweat glands (glandulce sudori/erm, figs. 565 and 567) have been 

 before dealt with, as far as relates to the differences of size and structure 

 observed among them (p. 357). 



The convoluted portion with which they commence is situated either 

 in the deeper parts of the corium, or more generally in the subcutaneous 

 areolar tissue, deeper than the hair follicles, and surrounded by the fat- 

 cells of the panniculus adiposus. The excretory duct, long or short, 

 according to the thickness of the corium, perforates the latter, passing 

 between the papillaa into the epidermis. In this course it frequently 

 twists and turns spirally, especially in the cuticle. The mouths of these 

 ducts, on the surface of the skin, are of microscopical minuteness, with 

 the exception of those on the palm of the hand and sole of the foot, 

 which are wider and funnel-shaped. Here they appear as rows of small 

 dots upon the ridges of the skin, whereas in other localities they present 

 themselves in irregular groups. Internally the glands in question are 

 lined sometimes with a single, sometimes double layer of round or poly- 



