512 



THE HUMAN EMBRYO. 



the hemispheres has greatly increased, and is now divided by a 

 median fold into right and left hemispheres, BS, which are 



VI 



vo 



TA 



VA 



FIG. 216. Human Embryo lettered by Professor His, Pr, and estimated as 

 twenty-eight days old. The brain is exposed from the left side ; and the 

 body of the embryo has been dissected to show the heart and aortic 

 arches, and the alimentary canal. (From His.) x 9. 



A, dorsal aorta. A.3, third aortic arch, or carotid arch. A.4, fourth aortic arch, or 

 systemic arch. A.5, fifth aortic arch, or pulmonary arch. BL, cerebellum. BM, 

 mid-brain. BS, cerebral hemisphere. IN, int'undibulum. KD, tireter. LG, lung. 

 LT, laryngeal chamber. OC, optic cup. PT, pituitary diverticulum from stomato- 

 daemn. B-B, left auricle. B/V, ventricle. TA, cavity of allantoic stalk. TO, cloaca. 

 TN, tongue. TR, intestine. TS, stomach. TZ, umbilical stalk. VA, allantoic 

 vein. VB, anterior cardinal vein. VC, posterior cardinal vein. VE, meatus veno- 

 sus. VI, posterior vena cava. VO, viti-lline vein. "W, liver. "WD, bile duct. 

 YK, yolk-stalk. 



already commencing to grow backwards over the thalamen- 

 cephalon. This latter is very deep dorso-ventrally, but com- 

 pressed laterally ; the infundibulum, IN, is of considerable size ; 



