LYMPHATIC GLAXDS. 191 



fibres in their parietes. Nerve-fibres, both dark-bordered and pale, have been 

 observed in the lyinph-hearts of the frog, and also nerve-cells in those of the 

 common toitoise (Waldeyer). 



Development of lymphatic vessels. — The cleTelopment of lymph- 

 atic capillaries has been studied by Klein in the serous membranes, 

 both normal and chronically inflamed. He finds that the process is 

 similar to that of the development of blood-vessels as described by him 

 in the chick. A vacuole is formed within one of the cells of the con- 

 nective tissue, and becomes larger and larger, so as to produce a cavity 

 filled with fluid, and vrith the protoplasm of the cell thinned out to 

 form the wall of the vesicle thus formed. From this protoplasmic 

 wall portions bud inwards into the cavity, eventually becoming de- 

 tached as lymph-corpuscles. Meanwhile "the nucleus of the cell has 

 become multiplied, and the resulting nuclei are regularly arranged 

 in the protoplasmic wall, which now exhibits, on treatment with 

 nitrate of silver, the well-known epithelioid marking characteristic 

 of the lymphatic capillaries. To form vessels, these vesicles become 

 connected with one another by means of processes into which their 

 cavities extend.* 



KoUiker has observed the formation of lymphatics from ramified cells in the 

 tails of young salamander-lan-fe. He states that the process takes place nearly 

 in the same manner as in the case of sanguiferous capillaries ; the only notable 

 difference being, that whilst the growing Ijonphatics join the ramified cells, and 

 thus extend themselves, their branches very rarely anastomose or become con- 

 nected by communicating arches. 



LYMPHATIC GLANDS. 



Lymphatic glands, named also conglobate, glands, and by modern 

 French wi-iters himpJmtic ganglions, are small solid bodies placed in the 

 course of the lymphatics and lacteals, 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, espe- 

 cially 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 

 groin. 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 lym- 

 phatic glands in their course, whilst, on 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 cells lining these l\Tuphatic vesicles, which are common in the mesogastrium o£ 

 the frog and toad in the winter season (owing to the existence of slight chronic inflam- 

 mation, a condition exceedingly prone to further the development of the lymphatic tissues), 

 bear, in the female of those animals, cilia directed inwards towards the cavity of the 

 vesicles. As the development into vessels proceeds, the ciha disappear (Klein), llemak 

 who first noticed these ciliated vesicles, took them for cysts in the membrane. 



