LYMPHATIC SYSTEM. 613 



the higher forms of these so-named lymphatic glands or 

 lymphatic ganglia. The few small lenticular bodies like 

 lymphatic ganglia observed in the neck of the roach have 

 been considered by some as mesenteric glands, and were 

 regarded by Meckel as the- first rudiment of the thymus 

 gland, which he considered, as well as the spleen, as merely 

 a lymphatic gland. Monro observed the deficiency of the 

 ordinary lymphatic glands in fishes, and considered the long 

 subcutaneous muciparous follicles as lymphatic vessels opening 

 by large orifices on the surface of their skin, and thence 

 supposed that all lymphatics must have similar open orifices. 



Besides extending as a continuous network over all the 

 deep-seated and superficial parts of fishes, they already 

 cover by their numerous plexuses, as shown by Fohmann, 

 the entire surface of the larger veins, especially when they 

 are distended with injected matter, and from the exten- 

 sibility of their soft thin coats, they generally appear very 

 wide and sacculated, and present numerous transverse con- 

 strictions of their parietes, at irregular distances, as if from 

 the commencing development of valves. The direct com- 

 munications of the lymphatics with many branches of veins 

 pointed out by Fohmann, have been more recently as- 

 cribed by Panizza and others, entirely to rupture of the 

 injected vessels and to transudation, not only in fishes but 

 in all higher classes. The large sacs and receptacles com- 

 monly observed on the injected lymphatics of fishes, are, 

 for the most part, produced by the pressure of the injected 

 matter on the thin distensible sides of these vessels. There 

 are commonly two great lateral plexuses of lymphatics 011 

 the trunk of fishes, passing forwards to terminate with the 

 anterior ventral plexus, in the thoracic ducts behind the 

 heart ; and the lymphatics of the head and dorsal parts of 

 the body enter the ducts anterior to this point, after forming 

 considerable plexuses near their entrance into the anterior 

 cav r a or into the jugular veins. The lymphatics from the 

 posterior parts of the body unite with the lacteals from the 

 intestine, to form two great trunks before ending in the re- 

 ceptaculum, which forms the commencement of the two 

 anastomosing plexiform wide thoracic ducts. They form a 

 compact layer of plexiform vessels around most of the organs 

 of the abdomen, as around the spleen, the large pancreatic 



