THE DEVELOPMENT OF THE VASCULAR SYSTEM. 291 



Where it is possible to obtain living embryos of some size, chicks for example, intra 

 vitam injections of the vessels afford instructive objects for study. While the heart is still 

 beating, India ink is injected into the liver by means of a small hypodermic syringe. The 

 ink is soon carried into the vessels. The embryo is fixed and the tissues then rendered more 

 or less transparent by putting in glycerin. 



The Heart. Chick embryos are taken during the first half of the second day of incu- 

 bation, fixed and sectioned as in the preparation for the study of blood vessels (see above). 

 Staining may be done with borax-carmin before embedding, or the sections may be stained 

 with haematoxylin. The double origin of the heart is clearly demonstrated in the sections 

 just behind the head region. 



Transverse sections taken at random through the heart in later stages are instructive, 

 but for a complete study recourse must be had to serial sections and plastic reconstructions. 



The Lymphatics. In any embryo prepared for the study of the bloodvessels (see above) 

 the lymphatic channels may be seen. It must be remembered, however, that the lymphatic 

 vessels do not begin to develop for some time after the appearance of the blood vessels 

 in the embryo (pig embryos of 12-15 mm.). Frequently it is difficult to distinguish the 

 lymphatic channels from veins, for both may contain blood cells. 



Developing lymph glands may be studied in the axilla and groin of foetal pigs which have 

 reached a length of 30 mm. and more. Serial sections prepared for the study of blood 

 vessels (see above) may be used; or the above mentioned regions may be cut from the fresh 

 embryo, fixed in Flemming's fluid, sectioned in paraffin and stained with Heidenhain's 

 haematoxylin. 



Very recently an ingenious scheme has been devised for injecting the vessels in embryos 

 with India ink (H. McE. Knower: A New and Sensitive Method of Injecting the Vessels of 

 Small Embryos, Etc., under the Microscope. Anat. Record, Vol. II, No. 5, 1908). 



References for Further Study. 



BERNAYS, A. C.: Entwickelungsgeschichte der Atrioventricularklappen. Morph. Jahr- 

 buch, Bd. II, 1876. 



BORN, G.: Beitrage zur Entwicklungsgeschichte des Saugetierherzens. Archiv. f. 

 mik. Anat., Bd. XXXIII, 1899. 



DISSE, J.: Die Entstehung des Blutes und der ersten Gefasse im Hiihnerei. Arch.}, 

 mik. Anat., Bd. XVI, 1879. 



ETERNOD, A. C. F.: Premiers stades de la circulation sanguine dans 1'oeuf et embryon 

 humain. Anat. Anz., Bd. XV, 1899. 



His, W.: Anatomic menschlicher Embryonen. Leipzig, 1880-1885. With Atlas. 



HOCHSTETTER, F. : Die Entwickelung des Blutgefasssystems. In Hertwig's Handbuch 

 der vergleich. und experiment. Entwickelungslehre . Bd. Ill, Teil II, 1901. Contains also 

 extensive bibliography. 



HOWELL, W. H. : The Life History of the Formed Elements of the Blood, Especially 

 the Red Blood-corpuscles. Journal of Morph., Vol. IV, 1890. 



HUNTINGTON, G. S.: The Genetic Interpretation of the Development of the Mammalian 

 Lymphatic System. Anat. Record, Vol. II, Nos. i and 2, 1908. 



HUNTINGTOX, G. S., and McClure, C. F. W.: Development of Postcava and Tribu 

 taries in the Domestic Cat. Am. Jour, of Anat., Vol. VI, 1907. 



HUNTINGTOX, G. S., and McClure, C. F. W.: The Development of the Main Lymph 

 Channels of the Cat in their Relations to the Venous System. Am. Jour, of Anat., Vol. VI, 

 1907. 



