462 Helen Williston Smith. 



thoraco epigastric as a very superficial vessel that may be seen plainly 

 in uninjected specimens, running from its forked origin near the 

 hind leg, along the milk ridge up to the manubrium at which point 

 it dips sharply down to enter the internal mammary vein. This 

 completes the history of the changes in the superficial blood vessels 

 of the body wall. 



During this development, four circulations obtained in the super- 

 ficial layers. First, the circulation in which the posterior cardinal 

 plays a part. Second, the circulation across the membrana re- 

 uniens to the umbilical vein ; then, thirdly, the formation and growth 

 of the thoraco epigastric and superficial epigastric on the outer side 

 of the muscle layer; and somewhat later, that of the internal mam- 

 mary veins and artery on the mesial side. The thoraco epigastric 

 grows with the superficial epigastric until they drain the whole 

 superficial body wall dorsalwards as far as the spinal cord. Mean- 

 while the internal mammary vessels have grown. The intercostal 

 veins and arteries also have been spun' out of the plexuses of the 

 segmental vessels, as the muscles and ribs invade the membrana 

 reuniens, and they anastomose with the anterior intercostals from 

 the internal mammary vessels. The internal mammary vein increases 

 in size. Its connections with the thoraco epigastric increase also, and 

 gradually the end of the thoraco epigastric is switched off, and we 

 reach the fourth and final stage in which the superficial body wall 

 drains largely into the internal mammary vein. After this con- 

 dition is reached further change is not so much in kind as in degree. 



REFERENCES. 



Balfour. F. M. Comiiarative Embryologj', II, 658. 



BUKOW. Archiv f. Aimt. ii. Pliys., 183S, S. 44. 



EcKER n. WiEDERSnEiN. Anatouiie cles Frosches, S. 413. 



His. Auat. inensch. P^uilu-youeii. Ill, S. 20B. also Fig. 130. 



His. Die anat. Noinenclatur. Leipzig, 1895. 



JoRis. Rechercbes sur les Veines Ombilicales et Para Ombilicales. Bull. 



de I'Acad. Royale de Medeciiie de Belgique, 1905. 

 KoLLiKER. Grundriss d. Entwickl. d. Meuscben, S. 103. Fig. 58, 1884. 

 Mall. Journal of Morpbology, XIV. p. 362, 1898. 

 Pfeifer. Zur Keuntnis des bistolog. Baues und der Riickbildung der 



Nabelgefiisse und des Duet. Bot. Arcb. f. Patb. Anat.. CLXVII. 

 Sappey. Veines portes accessoires. Jour, de I'Anatomie, XIX, 1883. 

 Wertheimer. Recbercbes sur la veine onibilicale. Jour, de I'Auat. et de la 



Pbys., XXII. 1886. 



