SUPRARENAL BODIES. 547 



Owing to the allantoic (anterior abdominal) vein having merely a foetal 

 existence an anastomosis between the iliac veins and the portal system by 

 means of the anterior abdominal vein is not established. 



Bibliography of the Venous System. 



(498) J. Marshall. "On the development of the great anterior veins." Phil. 

 Trans., 1859. 



(499) H. Rathke. "Ueb. d. Bildung d. Pfortader u. d. Lebervenen b. Sauge- 

 thieren." MeckeVx Archiv, 1830. 



(500) H. Eathke. "Ueb. d. Ban n. d. Entwick. d. Venensystems d. Wirbel- 

 thiere." Bericht. iih. 'd. naturh. Seminar, d. Univ. Konifjsberg, 1838. 



Vide also Von Baer (No. 291), Gotte (No. 396), Kolliker (No. 298), and Rathke (Nos. 

 299, 300, and 301). 



Lymphatic System. 



The lymphatic system arises from spaces in the general parenchyma 

 of the body, independent in their origin of the true body cavity, though 

 communicating both with this cavity and with the vasciilar system. 



In all the true Vertebrata certain parts of the system form definite 

 trunks communicating with the venous system ; and in the higher types 

 the walls of the main lymphatic trunks become quite distinct. 



But little is known with reference to the ontogeny of the lymphatic 

 vessels, but they originate late in larval life, and have at first the form of 

 simple intercellular spaces. 



The lymphatic glands appear to originate from lymphatic plexuses, the 

 cells of which produce lymph corpuscles. It is only in Birds and Mnmmals, 

 and especially in the latter, that the lymphatic glands form definite 

 structures. 



The Spleen. The spleen, from its structure, must be classed with the 

 lymphatic glands, though it has definite relations to the vascular system. 

 It is developed in the mesoblast of the mesogastrium, usually about the 

 same time and in close connection with the pancreas. 



According to Miiller and Peremeschko the mass of mesoblast which 

 forms the spleen becomes early separated by a groove on the one side from 

 the pancreas and on the other from the mesentery. Some of its cells 

 become elongated, and send out processes which uniting with like pro- 

 cesses from other cells form the trabecular system. From the remainder 

 of the tissue are derived the cells of the spleen pulp, which frequently 

 contain more than one nucleus. Especial accumulations of these cells take 

 place at a later period to form the so-called Malpighian corpuscles of the 

 spleen. 



Bibliography of Spleen. 



(501) W. Miiller. "The Spleen." Strieker's Histology. 



(502) Peremeschko. "Ueb. d. Entwick. d. Milz," Sitz. d. Wieii. Akad, Wiss., 

 Vol. Lvi. 1867. 



Suprarenal bodies. 



In Elasmobranch Fishes two distinct sets of structures are found, both 

 of which have been called suprarenal bodies. As shewn in the sequel 



the heart through the liver is aborted, and the ductus venosus Arantii is a secondary 

 connection established in the latter part of foetal life. 



35—2 



