THE HEAET, 



567 



ear-like appendages. A marked constriction, the canalis auri- 

 cularis, separates it from the ventricular portion. This latter 

 RV, is shaped something like the adult stomach, and lies almost 



Fie. 243. — Human Embryo, lettered by Professor His, Bl, and estimated as 

 twenty-three days old. The brain and spinal cord are exposed from the 

 right side ; and the body is dissected to show the heart, the blood-vessels, 

 and the alimentary canal. (From His.) x 20. 



A, dorsal aorta. A. 2, second aortic arch, in the hyoidean arch. A.3, third aortic, or 

 carotid arch, in the first brancliial arch. A.4, fourth aortic, or systemic arch, in the 

 second branchial arch. A.5, fifth aortic, or pulmonary arch, in the third branchial arch. 

 AP, pulmonary ai-tery. BL, cerebellum. BM, mid-brain. BS, cerebral hemisphere. 

 CH, notochord. EI, ear. IN", infundibulum. KC, WolflBan duct. KD, ureter. 

 LG, lung. OC, optic cup. PT, pituitary body. RA, right auricle. TI, intestine 

 TW", tongue. TR, rectum. TS, stomach. VD, Cuvierian vein. V V , vitelline vein 

 YK, yoIk-stalk. 



directly across the body ; its right-hand or distal end bends 

 sharply forwards, and passes into the truncus arteriosus, KT, 

 ■which is attached to the floor of the fore-gut rather further back 



