382 LYMPHATIC SYSTEM. 



posterior pair, situated in the sciatic region, which pour their lymph into a branch of the 

 sciatic or of some other neighbouring vein, and an anterior more deeply -seated pair, placed 

 over the transverse process of the third vertebra, and opening into a branch of the jugular 

 vein. The parietes of these sacs are thin and transparent, but contain muscular tissue, which 

 here and there appears obscurely striated, decussating in different layers, as in the blood-heart. 

 In their pulsations they are quite independent of the latter organ, and are not even syn- 

 chronous with each other. In salamanders, lizards, serpents, tortoises, and turtles, only a 

 posterior pair have been discovered, which, however, agree in all essential points with those of 

 the frog. In the goose, and in other species of birds belonging to different orders, Panizza 

 discovered a pair of lymph-sacs opening into the sacral veins, and Stannius has since found 

 that these sacs have striated muscular fibres in their parietes. Nerve-fibres, both dark-bordered 

 and pale, have been observed in the lymph-hearts of the frog, and also nerve-cells in those of 

 the common tortoise (Waldeyer). 1 



Development of lymphatic vessels. The development of lymphatic 

 capillaries has been studied by Klein in the serous membranes. He finds that the 

 process is similar to that of the development of blood-vessels. A vacuole is formed 

 within one of the cells of the connective tissue, and becomes gradually larger, so as 

 ultimately to produce a cavity filled with fluid, with the protoplasm of the cell 

 thinned out to form the wall of the vesicle thus produced. From this protoplasmic 

 wall portions are said to bud inwards into the cavity, eventually becoming detached 

 as lymph corpuscles ; it is more probable, however, that the lymph corpuscles 

 which are seen in the developing lymphatics have " wandered in," as in the case of 

 the white corpuscles of the blood. 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 wavy epithelial 

 marking characteristic of the lymphatic capillaries. To form vessels, the vesicles 

 become connected with one another by means of processes into which their cavities 

 extend. 



The cells lining these lymphatic vesicles, which are common in the mesogastrium of the 

 frog and toad in the winter season bear, in the female of those animals, cilia directed inwards 

 towards the cavity of the vesicles. As the development into vessels proceeds, the cilia 

 disappear (Klein). Remak, who first noticed these ciliated vesicles, took them for cysts in the 

 membrane. 



LYMPHATIC GLANDS. 



Lymphatic glands, formerly named also conglobate glands, and by modem 

 French writers lymphatic 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 alongside of the great vessels of the neck, and also in the 

 thorax and abdomen, especially in the mesentery and alongside of 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. 



The lymph of some lymphatic vessels has to traverse two, three, or even more 

 lymphatic glands before reaching the thoracic duct, whilst, on the other hand, there 

 are lymphatics which enter the thoracic duct without having traversed any gland in 

 their way. 



The size of lymphatic glands is very various, some being not much larger than 



1 Miiller's description is to be found in the Philosophical Transactions for 1833 ; Panizza's in a special 

 memoir on the Lymphatic System of Reptiles, published in the same year. For a more complete account 

 of the lymphatic hearts of the frog, the reader is referred to the " Le9ons d'Anatomie Generale," 

 delivered by Prof. Ranvier in the College de France in 1877-78, and published in 1880, and to the 

 " Trait6 Technique " of the same author, 2nd edition, published in 1889. 



