520 LYMPHATIC GLANDS. [BOOK n. 



take on the form of more or less pyramidal blocks, in the medulla 

 the follicular substance is arranged in the form of branching and 

 anastomosing cords, the medullary cords, surrounded by a tubular 

 branching and anastomosing jacket of lymph-sinus. At the junction 

 of the cortex and medulla the follicles of the alveoli of the former 

 branch off into and become the medullary cords of the latter, and 

 the lymph-sinuses of the former are similarly continuous with the 

 labyrinth of lymph-sinuses of the latter. 



The gland in fact may be considered as consisting of three 

 parts : the skeleton supplied by the capsule and trabeculse and 

 dividing the interior of the gland into the regular alveoli of the 

 cortex and the labyrinth of the medulla ; the follicular substance 

 occupying the centre both of the alveoli and of the labyrinth and 

 continuous throughout both, as if it had originally filled up the 

 whole of the spaces of the skeleton and had subsequently shrunk 

 away on all sides ; and lastly the lymph-channel occupying all the 

 spaces left between the follicular substance and the skeleton, and 

 thus forming a labyrinth of its own throughout the gland. 

 Obviously a lymphatic gland is a consolidated and differentiated 

 collection of lymphatic follicles or Peyer's patch. In a Peyer's 

 patch each follicle is distinct and independent; in a lymphatic 

 gland the follicles are fused together, partially so in the cortex but 

 completely so in the medulla. 



The afferent lymphatic vessels, which are small or medium 

 sized vessels with the structure described in 286, after forming a 

 plexus between the two layers of the capsule open out into the 

 lymph-sinuses of the alveoli beneath the cortex; these lymph- 

 sinuses are practically lymph-capillaries into which the regular 

 afferent lymphatic vessels break up. The efferent lymphatic 

 vessels are similarly connected with the lymph-sinuses of the 

 medulla at the hilus; here the lymph-capillaries of the me- 

 dulla open into and form the regular lymphatic vessels which 

 issue from the gland at this point. In the afferent vessels the 

 lymph is flowing, as we shall see, at a certain rate and under a 

 certain pressure ; it continues to flow through the labyrinth of the 

 lymph-sinuses of the gland, bathing as it flows the follicular 

 substance, its course being retarded by the reticulum of the 

 lymph-sinuses ; it finally issues by the efferent vessels. 



The small arteries entering the gland at the hilus run along 

 the skeleton of trabeculae, dividing as they go ; at intervals they 

 send off small branches which, leaving the trabecular support, 

 traverse the lymph-sinus and plunging into the follicular substance 

 break up into capillaries. By far the greater part of the blood 

 sent to the gland thus runs in capillary networks in the follicular 

 substance of the alveoli and medulla. From these capillaries the 

 blood finds its way back by veins through the lymph- sinus to the 

 trabeculse, and so issues from the gland at the hilus. 



293. Obviously here, as in the lymphatic follicle of the in- 



