78 GENERAL ANATOMY. 



With respect to the structure of the Lymphatic Glands, there are some points 

 which are certain, while others must be allowed to be doubtful. It is certain 

 that a number of vessels enter them at various points of their circumference 

 (afferent vessels), and that one or two vessels leave them (efferent vessels), usually 

 at a definite spot, the hilum. Further, that the external coats of these vessels 

 are continuous with an envelope of fibrous tissue, which constitutes the capsule 

 of the gland, and that all parts of the gland are freely supplied with capillary 

 bloodvessels. The intimate structure, however, of the gland, is a matter of 

 some doubt. In former editions of this work, the description of Hewson was 

 adopted, according to which the afferent vessels break up into a plexus of 

 smaller vessels, and these reunite to form the efferent vessels, so that the 

 afferent and efferent lymphatics are directly continuous. Some observers 

 added to this description, that there were a number of minute dotted cor- 

 puscles lying between the meshes of the network of vessels in the interior of 

 the gland, and grouped in cells like the acini of secreting glands. 



But the description given by His and Kolliker, and which has been adopted 

 by Dr. Sharpey, makes the structure more complex than this. It is, in brief, as 

 follows: Passing inwards from the capsule of the gland are a number of septa 

 or trabecula3, fibrous in man, muscular in some of the lower animals, which 

 separate the outer or cortical portion of the gland into alveoli. The afferent 

 vessels break up and open into these alveoli, much in the same way that the 

 splenic capillaries open into the pulp of that organ. The alveoli contain a 

 grayish-white pulp, consisting, according to Kolliker, of the minutest ramifica- 

 tions of fibrous tissue, and of a juice, containing round cells identical with those 

 of the chyle or lymph. 



The interior of the gland (medullary portion) is formed of a number of vascular 

 channels (together with capillaries and connective tissue), which are the radi- 

 cles of the efferent vessels, and converge to the hilum. The cortical portion is 

 usually deficient at the hilum, where the medullary tissue of the gland passes 

 directly into the efferent channels. 



The afferent lymphatics, after passing at various points through- the capsule, 

 break up in the septa between the alveoli into their terminal ramifications; and 

 here, as Kolliker supposes, they open into those spaces just as the arteries of 

 erectile tissue do into the cavernous spaces of which that tissue is composed. 

 From the walls of the alveoli lymphatic channels can again be traced, which are 

 the radicles of the efferent vessels, and accompany the arterial branches. 



The gland-pulp does not completely fill the alveoli of the cortical, nor th( 

 vascular channels of the medullary portion, but leaves a space, visible in sec 

 tions from which the lymph-corpuscles have been washed away. This space is 

 called the lymph-sinus; but it seems to be distinguished from the rest of the 

 alveolus merely by a less close arrangement of the connective tissue, through 

 which the lymph circulates. Dr. Sharpey describes the lymph-sinus as lined 

 throughout by a layer of pavement-epithelium similar to that of the lymphatic 

 vessels with which it is continuous. 



The arteries and veins pass into and out of the gland at the hilum, and Kol- 

 liker has described some fine nervous filaments, as accompanying them. 



THE SKIN AND ITS APPENDAGES. 



The Skin is the principal seat of the sense of touch, and may be regarded as 

 a covering for the protection of the deeper tissues; it is also an important 

 excretory and absorbing organ. It consists of two layers, the derma or cutis 

 vera, and the epidermis or cuticle. On the surface of the former layer are the 

 sensitive papillae; and within, or imbedded beneath it, are the sweat-glands, 

 hair-follicles, and sebaceous glands. 



The derma, or true skin, is tough, flexible, and highly elastic, in order to de- 

 fend the internal parts from violence. It consists of fibro-areolar tissue, inter- 



