OBSERVATIONS ON THE LIVING EGG. 487 



Fig. 94. A Chick Embryo at the end of the third day of incubation. 

 Owing to the twisting of the fore part of the embryo, the head and 

 neck are seen from the right side, and the hinder part of the body 

 from the dorsal surface. The amnion has been removed, x 20. 



A, dorsal aorta. A 1 , first or mandibular aortic arch. A 3, third aortic arch, 

 in the first branchial arch. AC, carotid artery. AV, vitelline artery. BF, 

 thalamencephalon or fore-brain. BH, medulla oblongata. BL, cerebellum. 

 BM, mid-brain. BS, cerebral hemisphere. El, auditory vesicle. HC 1, first 

 branchial cleft. HC 2, second branchial cleft. HM, hyo-mandibular cleft. 

 MS, mesoblastic somite or protovertebra. NS, spinal cord. OC, optic cup. 

 OF, olfactory pit. OL, lens. PN, pineal body. RA, auricle of heart. RT, 

 truncus arteriosus. RV, ventricle of heart. VV, vitelline veins. 



