The Origin and Development of the Lymphatic System. 83 



The fundamental morphology of the lymphatic system has been es- 

 tablished, but there remain many gaps in our knowledge of the system 

 as a whole. The deep lymphatics in amphibia and reptilia are almost 

 unknown ; in fact a complete account of the lymphatic systems in 

 both of these groups would be of great value. In birds the origin of 

 the iliac lymphatics and the growth of the thoracic duct would be most 

 interesting. In mammals the gaps in our knowledge are especially 

 in regard to the development of the lymphatic system within many 

 of the organs; for example, the heart and lungs, the liver, spleen, 

 kidneys and reproductive organs. A study of the embryology of the 

 lymphatic system makes it more certain that the central nervous 

 system has no lymphatics. The lymphatics invade the body, but not 

 completely; the nervous system is a permanent non-lymphatic area. 



It is now possible to define the lymphatics. Lymphatic capillaries 

 are tubes of endothelium; they are derived from the endothelium of 

 the veins, and they have the same relation to tissue spaces as have 

 blood capillaries. 



LlTEEATUEE. 



1. Abel, J. J. : On the action of drugs and the function of the 



anterior lymph hearts in cardiectomized frogs. Journ. of 

 Phar. and Exp. Ther., Vol. 3, 1912. 



2. Allen, W. F. : Distribution of the lymphatics in the head, and 



in the dorsal, pectoral, and ventral fine of Scorpamichthys 

 marmoratus. Proc. Wash. Acad, of Science, Vol. 7, 1906. 



3. Distribution of the subcutaneous vessels in the tail 



region of Lepisosteus. Amer. Journ. of Anat., Vol. 8, 1908; 

 Anat. Record, Vol. 2, 1908. 



4. Distribution of the lymphatics in the tail region of 



ScorpEenichthys marmoratus. Amer. Journ. of Anat., Vol. 

 11, 1910-1911. 



5. Arnold, J.: Experimentelle Untersuchungen ueber die Ent- 



wickelung der Blutcapillaren. Arch, fiir path. Anat., Bd. 53, 

 1871 and Bd. 54, 1872. 



6. Ueber die Beziehung der Blut- und Lymphgefasse zu 



den Saftkanalen. Arch, fiir path. Anat., Bd. 63, 1875. 



7. v. Baek: Entwickelungsgeschichte der Tiere. I. Teil, 1828. 



II. Teil, 1837. 



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