300 THE LYMPHATIC SYSTEM, BY F. v. RECELIXGHAUSEN. 



organs, the surface which is turned towards the interior of 

 the cavity being covered with a single layer of tesselated epi- 

 thelium. Only such septa as divide the several lymph spaces 

 from each other, and are composed of pure connective tissue, 

 can be regarded as properly belonging to them. The lymph 

 sacs in these animals therefore resemble the peritoneal and 

 pleural sacs, with this difference, that the lymph sacs commu- 

 nicate with one another by means of microscopic openings in 

 their septa, and consequently form a continuous system of 

 cavities. Inasmuch as the lymph sacs are almost entirely 

 destitute of proper walls, the muscular elements, 5 the function 

 of which is to aid in the propulsion of the lymph, also fail ; 

 but in their stead special contractile organs, acting rhythmically, 

 appear in certain parts of the lymphatic system of Amphibia. 

 These constitute the lymph hearts discovered by J. Miiller, and 

 one of them lying posteriorly near the sacrum propels the 

 lymph into the sciatic vein, whilst the anterior pumps it into 

 a branch of the jugular. They are chiefly composed of trans- 

 versely striated short muscular laminae. 



These peculiarities in the structure and arrangement of the 

 large lymphatics of Amphibia in contrast with those of other 

 Vertebrata, are of great interest. They prove clearly that great 

 variability occurs in the lymphatic system, much greater even 

 than in the blood vascular system; and, in truth, this variability 

 occurs not only in different classes of animals, but in one and the 

 same species, and not only in the larger trunks, but in the smaller 

 vessels. The number and size of the principal trunks of any 

 organ, as, for example, of one of the extremities of man, pre- 

 sents as little constancy as the mode of their division. Even 

 in one and the same organ the results of injection are often 

 quite different, and it frequently happens that injections of the 

 same organs in nearly allied animals present such remarkable 

 differences, that only the most general statements can be made 

 in reference to the arrangement of the lymphatics of any par- 

 ticular locality.* It is obvious, -therefore, that those typical 

 modes of arrangement which occur in the arterial and capillary 

 blood vascular systems of the different organs can only be im- 



* See the illustrations in L. Teiehmann's Saugader system. Leipzig, 1861. 



