512 



THE HUMAN EMBKYO. 



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

 median fold into right and left hemispheres. By, which are 



RB 



BL 



IN 



LG 



TS 



YC 



WD 



V, 



TA 



FIG. 21(j. 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. tliird aortic arch, or carotid arch. A.4, fourth aortic arch, or 

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

 mid-brain. BS, cerebral hemisphere. IN", infundibulum. KD, ureter. LG, lung. 

 LT, larynscal chamber. OC. optic cup. PT. pituitary dlverticuluin from stomato- 

 dteum. RB, If ft auricle. RV, ventricle. T A, cavity of allantoic stalk. TC, cloaca. 

 TN, tonpuu. 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, vitc-llinu .voin. "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; 



