LYMPHATICS OF THE HEAD AND NECK. 353 



times instead of being circular the aperture is elliptical, and the arrange- 

 ment of the flaps like that of the ileo-coecal valve.* These peculiarities 

 are most frequently met with at and near the anastomoses of the lymphatic 

 vessels. The valves occur most numerously near the lymphatic glands ; 

 next in frequency they are found in the neck and upper extremities, where 

 the vessels are small, and least numerously in the lower limbs, where the 

 lymphatics are larger. In the thoracic duct an interspace of two or three 

 inches frequently occurs between the valves. Connected with the presence 

 of valves in the lymphatic vessels, are two lateral dilatations or pouches, 

 analogous to the valvular sinuses of veins. These sinuses are situated on 

 the cardiac side of the valves ; they receive the valves when the latter are 

 thrown back by the current of the lymph ; and when reflux occurs, they 

 become distended with a body of fluid which makes pressure on the flaps. 

 These pouch-like dilatations and the constrictions corresponding with the 

 line of attachment of the convex borders of the flaps are the cause of the 

 knotted appearance of distended lymphatic vessels. 



Like arteries and veins, lymphatic vessels are composed of three coats, 

 external, middle, and internal. The external coat is areolo-fibrous, like 

 that of blood-vessels ; it is thin, but very strong, and serves to connect 

 the vessel to surrounding tissues, at the same time that it forms a protec- 

 tive covering. The middle coat is thin and elastic, and consists of a layer 

 of longitudinal fibres analogous to those of the innermost layer of the 

 middle coat of arteries and veins. Some few circular fibres may be seen 

 externally to these in the larger, lymphatic vessels. The internal coat is 

 inelastic and more liable to rupture than the other coats. It is a serous 

 layer continuous with the lining membrane of the veins, and invested by 

 an epithelium. The valves are composed of a very thin layer of fibrous 

 tissue, coated on its two surfaces by epithelium. 



The lymphatic glands (conglobate, absorbent) are small oval and some- 

 what flattened or rounded bodies, composed of a plexus of minute lym- 

 phatic vessels, associated with a plexus of blood-vessels, and enclosed in 

 a thin capsule of areolar tissue. When examined on the surface, they 

 are seen to have a tabulated appearance, while the face of a section is 

 cellular, from the division of the numberless convolutions which are formed 

 by the lymphatic vessels within its substance. The colour of the glands 

 is a pale pink, excepting those of the lungs, the bronchial glands, which in 

 the adult are more or less mottled with black, and are sometimes filled 

 with a black pigment. Lymphatic glands are larger in the young subject 

 than in the adult, and are smallest in old age ; they, as well as their ves- 

 sels, are supplied with arteries, veins and nerves, like other structures. 



I shall describe the lymphatic vessels and glands according to the 

 arrangement adopted for the veins, commencing with those of the head 

 and neck, and proceeding next to those of the upper extremity, lower ex- 

 tremity, and trunk. 



LYMPHATICS OF THE HEAD AND NECK. 



The Superficial lymphatic glands of the head and face are small, few in 

 number, and isolated ; they are, the occipital, which are situated near the 

 origin of the occipito-frontalis muscle ; posterior auricular, behind the 

 ear ; parotid, in the parotid gland ; zygomatic, in the zygomatic fossa , 



* Mr. Lane, loc. cit. 



30* x 



