512 



THE HUMAN EMBRYO, 



tlie hemispheres has greatly increased, -and is now divided by a 

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



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 arcli. A.4, fourth aortic arch, or 

 systemic arch. A.5, fifth aoi-tic arch, or pulmonary arch. BL, cerebellum. BM, 

 mid-brain. BS, cerebral hemlsjiliere. IW, infundibulum. KD, ureter. LG-, lung, 

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

 daaum, BB, left auricle. BV, ventricle. T A, cavity of allantoic stalk. TC, cloaca. 

 TN, tongue. TE, intestine. TS, stomach. TZ, umbilical etaUc. VA, allantoic 

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

 sus. "VI, ijosterior vena cava, VO, vitelline 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 ; 



