clsxxvi LYMPHATIC SYSTEM. 



the dog's pleura, by which the superficial lymphatics open on the surface of the mem- 

 brane; he also found that fine particles of colouring matter could, under certain con- 

 ditions, be made to pass from the cavity of the pleura into the lymphatics, and appa- 

 rently by the openings in question.* 



^Respecting these observations, however, it must be remarked, that the apertures 

 described do not open upon a surface in contact with extraneous matters, as that of 

 the skin or a mucous membrane, but into a serous cavity ; and perhaps they may be 

 explained on the supposition that the peritoneum, pleura, and other serous sacs, are 

 really large lymph-lacunae, from which lymphatic vessels lead out as emissaries, as in 

 the case of the subcutaneous lymph-spaces of the frog, and the testicular and other 

 lymph lacunae constructed on a smaller scale. 



Absorbent or lymphatic glands, named also conglobate glands, and by 

 modern French writers lymphatic ganglions, are small solid bodies placed in 

 the course of the lymphatics and lacteal*, through which the contents of 

 these vessels have to pass in their progress towards the thoracic or the 

 right lymphatic duct. These bodies are collected in numbers along the 

 course of the great vessels of the neck, also in the thorax and abdomen, 

 especially in the mesentery and alongside the aorta, vena cava inferior, and 

 iliac vessels. A few, usually of small size, are found on the external parts 

 of the head, and considerable groups are situated in the axilla and gioiu. 

 Some three or four lie on the popliteal vessels, and usually one is placed a 

 little below the knee, but none farther down. In the arm they are found 

 as low as the elbow-joint. 



Lymphatic vessels may pass through two, three, or even more lymphatic 

 glands in their course, whilst, ou the other hand, there are lymphatics which 

 reach the thoracic duct without encountering any gland in their way. 



The size of these bodies is very various, some being not much bigger 

 than a hempseed, and others as large or larger than an almond or a kidney- 

 bean. In shape, too, they present differences, but most of them are round 

 or oval. 



The lymphatics or lacteals which enter a gland are named inferent or 

 afferent vessels (vasa infer entia sen afferentia), and those which issue from 

 it efferent vessels (vasa efferentia). The afferent vessels, on approaching a 

 gland, divide into many small branches, which enter the gland ; the 

 efferent vessels commonly leave the gland in form of small branches, and at 

 a little distance beyond it, or sometimes even before issuing from it, unite 

 into one or more trunks, usually larger in size but fewer in number than 

 those of the afferent vessels. 



The internal structure of lymphatic glands has been long a subject of 

 inquiry. Hewson considered that a lymphatic gland essentially consists of 

 a network of finely divided lymphatic vessels, on and between which capil- 

 lary blood-vessels are ramified ; the whole being gathered up and compacted 

 into a comparatively dense mass by connective tissue, which at the surface 

 of the gland forms for it an inclosing capsule. The afferent and efferent 

 vessels are, according to Hewson, continuous with each other within the 

 gland, and the cellular cavities described as intervening between them and 

 serving as the medium of their communication, were held by him to be 

 nothing more than partial dilatations of some branches of the common con- 

 necting plexus. 



Hewson's view of the constitution of the lymphatic glands was, till 



* Bericbte der K. Sachs. Gesellsch. der Wissensch. July, 1866, p. 191. In the 

 same publication, p. 247, is an account, by F. Schweigger-Seidel and J. Dogiel, of open 

 communications between the frog's peritoneum and the great lymph-sac (cisterna magna) 

 behind it ; also founded on observations made in the Physiological Institute of Leipsic. 



