294 COMPARATIVE ANATOMY. 



of a paired organ lying on either side of the fauces, that is, in the 

 region where the mouth passes into the pharynx : they consist of 

 a retiform (adenoid) connective-tissue ground-substance enclosing 

 a number of lymph-corpuscles, which are arranged in so-called 

 follicles. 



Lymphoid tissue plays a very important part in the body-cavity 

 of Fishes and Amphibia. Apart from the alimentary canal, it is 

 present in considerable quantity in the region of the urinary and 

 genital glands, which are often regularly embedded in it (e.g. Dipnoi). 

 The mass of lymphoid tissue on the heart of the Sturgeon, and 

 possibly also the so-called "fat-bodies" of Amphibia and Rep- 

 tilia, and the " hibernating gland " of certain Rodents, may be 

 placed in this category. 



The agglomeration of a number of these follicles gives rise to 

 those structures which are spoken of as "lymphatic glands." 

 These are always interposed along the course of a lymphatic 

 trunk so that an afferent and efferent vessel to each can be dis- 

 tinguished. They probably appear first in Birds, and are most 

 numerous in Mammals, where they are present in abundance in 

 various regions of the body ; they differ greatly in size. 



The spleen, which is present in almost all Vertebrates, is 

 closely related to these structures. It usually lies near the 

 stomach, though it is occasionally met with in other regions of 

 the intestinal tract, as, for instance, at the commencement of the 

 rectum (Anura, Chelonia). In some cases (e.g. Sharks) it is broken 

 up into a number of smaller constituents. 



Both the lymphatic glands and the spleen have to do with the 

 formation of lymph-cells, but their complete physiological function 

 is as yet by no means clear. 



BIBLIOGRAPHY. 



AYERS, H. Beitr. zur Anatomie und Physiologic dcr Dipnocr. Jcna'sclie Zeitschrift 

 fur Naturwissenschaflen, Bd. XVIII. N. Folge, Bd. XI. 1885. 



BEDDARD, F. E. Note on the Presence of an Anterior Abdominal Vein in Echidna. 

 Proc. Zool. Soc. 1884. On the Heart of Apteryx. Ibid. 1885. 



BOAS, E. V. See numerous Papers On the Vascular System of Fishes and Amphibia 

 in the MorphoL Jahrb. Bd. VI. 1880, Bd. VII. 1881, and Bd. VIII. 1882. 



GOMPERTZ, C. Ucber Herz und Blutkreislauf bei nackten Amphibien. Arch. f. 

 Anat. und Physiologic (Physiologische Abtheilung), 1884. (This contains u 

 masterly description of the Anatomy and Physiology of the Heart of Anura.) 



LANKESTER, E. RAY. On the Valves in th, Heart of Ornithorhynchus paradoxus 

 compared with those of Man and the Rabbit, with some Observations on the Fossa 

 Ovalis. Proc. Zool. Soc. 1882. On the Right Cardiac Valve of Echidna anil. 

 Ornithorhynchus. Ibid. 1883 On the Heart described by Professor Owen in 

 1841 oa that of Apteryx. Ibid. 1885. On the Right Cardiac Valve of the Specimen* 

 of Apteryx disserted by Sir Richard Owen in 1841. Ibid. 1885. 



MASCAGNI. Prodome d'un oitvrage sur lesystemedes vaisseaux lymphatiques. Sienne, 

 1784. Vasorum lymphaticorum corporis humani historia et iconographia. 

 Senis, 1787. 



MiJLLER, J. Ucber die Lymphhcrzen dcr Amphibien. Arch. f. Anat. u. Phyr-ioL 

 1854. 



MULLER, W. -Ucbcr d<:n fcincren Ban dcr MHz. Leipzig, 1865. 



