THE LYMPH VASCULAB SYSTEM. 995 



The student should, therefore, acquaint himself with the various groups of 

 glands, with their afferents .and efferents, and with the exact position and relations 

 of the large lymphatic trunks ; he will then be in a position to understand the 

 course which minute organisms or particles, which have gained access to the lymph 

 spaces, may take as they are carried in the lymph stream ; and he will realise that 

 such structures may either be entangled in the glands through which the lymph passes, 

 or, having escaped all obstructions, that they will finally enter the veins at the root 

 of the neck. At the same time, if he bears in mind the existence of the numerous 

 anastomoses between the lymph vessels, he will have no difficulty in appreciating that 

 variations from any regular course may not infrequently occur, and his clinical ex- 

 perience at a later period will show that such variations are by no means uncommon. 



Structure of Lymph Glands. Lymph glands consist of (1) a skeleton or framework, 

 (2) lymph sinuses, and (3) lymph follicles and cords ; and each gland is separable into cortex and 

 medulla. The cortex lies immediately internal to the capsule, except at the hilum, where it is 

 absent. The medulla forms the internal part of the gland, and reaches the surface at the hilum. 



(1) The skeleton or framework consists of a capsule and of primary, secondary, and tertiary 

 trabeculse. 



The capsule is formed of white fibrous tissue, interspersed with elastic fibres, and in some cases 

 with unstriped muscular fibres. 



The primary trabeculce spring from the deep surface of the capsule and radiate through the 

 cortex into the medulla. In the cortex they are flattened lamellae, but as they reach the medulla 

 they break up into flattened, rounded, and angular bands which unite freely together ; 

 their structure is the same as that of the capsule, and from their surfaces the secondary 

 trabeculse are given off. The secondary trabeculce spring from the surfaces of the primary 

 trabeculse, cross the lymph sinuses and enter the follicles of the cortex and the cords of the 

 medulla, where they terminate by dividing into tertiary trabeculse. As they cross the lymph 

 sinuses they unite together freely, forming a fine mesh -work through which the lymph 

 passes in its course from the afferent to the efferent vessels. The secondary trabeculse consist 

 of fine strands of fibrous tissue devoid of nuclei. The tertiary trabeculce are finer and more 

 delicate than the secondary trabeculse, from the terminations of which they spring, but they 

 have a similar structure. They unite together, forming a fine network in the lymph cords and 

 follicles, and the spaces of the network are filled with lymph corpuscles. The surfaces of the 

 trabeculse which bound the lymph sinuses are covered with endothelial cells. 1 



(2) The lymph sinuses lie internal to the capsule and around the primary trabeculse which 

 form their boundaries on one side, whilst on the other they are limited by the lymph cords 

 and follicles. They are traversed by the secondary trabeculse, and their channels are thus 

 converted into a kind of sponge- work through which the lymph stream flows. In the cortical 

 parts of the glands they form more or less cylindrical channels, but in the medulla they become 

 moniliform. Afferent vessels enter the sinuses of the cortex, and the efferent vessels emerge from 

 the medulla at the hilum. 



The lymph, follicles lie in the cortical portions of the lymph glands, where they form the 

 inner boundaries of the lymph sinuses. They consist of dense masses of lymphoid cells, embedded 

 in a stroma formed by the tertiary trabeculae, and they are continuous internally with the 

 lymph cords of the medullary substance. 



The lymph cords are continuous with the lymph follicles, and have the same structure, but 

 they lie in the medullary portions of the glands ; they are cord-like and not nodular in shape, 

 and they form the peripheral boundaries of the lymph sinuses of the medulla. 



The Blood- Vessels of the Lymph Glands. Blood-vessels are distributed to the capsule and 

 through the capsule to the primary trabeculae of the glands ; but the main blood-vessels to each 

 gland enter the hilum and ramify in the lymph cords and follicles, amidst the tertiary trabeculse 

 which are connected with the walls of the vessels. 



Haemal Lymph Glands. In various parts of the body, but more particularly in 

 the retro-peritoneal region, and especially along the line of .the abdominal aorta, a 

 number of bodies may be found which have all the ordinary structural characters 

 of lymph glands, but they differ from lymph glands inasmuch as some of their 

 sinuses contain blood. These structures are called haemal lymph glands. The 

 sinuses of the hsemal lymph glands which contain lymph are in continuity with 

 lymphatics, whilst the blood-filled sinuses open into blood-vessels. It is stated 

 that communications exist between the blood and the lymph containing sinuses of 

 the haemal lymph glands, but the evidence on this point is not quite satisfactory. 



Hsemal Glands. The term " hsemal gland " is applied to nodules possessing the 

 structure of ordinary lymph glands, but which contain only blood in their sinuses ; 

 they probably belong, however, as their development shows, to the lymph vascular 

 and not to the blood vascular system (see p. 1042). 



1 See p. 1059. 



64 a 



