THE HEART. 



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 



AP A.5 



VD 



A. 3 



T,M 



El 



YK 



KD 



CH 



FIG. 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 branchial 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 artery. BL, cerebellum. BM, mid-brain. BS, cerebral hemisphere. 

 CH, notochord. EL ear. IN, infundibulum. KC, Wolllian duct. KD, ureter. 

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

 TN, tongue. TB, rectum. TS, stomach! VD, Cuvierian vein. W, vitelline vein 

 YK, yolk-stalk. 



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

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

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



