500 



THE HUMAN EMBRYO. 



meatus. The tuberculum lobulare (e) fuses with the lower end 

 of the Cauda helicis (Pig. 209), and at a later stage grows 

 ventralwards to give rise to the lobule of the ear. The tubercula 

 anthelicis, tragicum, and antitragicum, give rise to the antihelix, 

 tragus, and antitragus respectively of the adult ear. 



The body of the embryo presents no external characters of 

 special interest during the fifth week. Owing to the increasing 

 thickness of the muscular and connective tissue walls, the out- 

 lines of the internal organs are less distinctly seen from the 

 surface than in the earlier stages. 



The limbs undergo important changes during the week, and 



Fig. 208. 



Fig. 209. 



Fig. 208. — The left ear of a Human Embryo lettered by Professor His, Br.2„ 

 and estimated as thirty-five days old. (From His.) x 20. p 



Fig. 209. — The left ear of a Human Embryo, lettered by Professor His^ Dr, 

 and estimated as thirty-eight days old. (From His.) x 20. 



1, tuberculum tragicum. 2, tuberculum anterms helicis. 3, tuberculum inter- 

 medium helicis. 3c and c, Cauda helicis. 4, tuberculum anthelicis. 5, tuberculum anti- 

 tragicum. 6, tuberculum lobulare. 



afford ready means of determining the age of the embryo. In 

 the early part of the fifth week they become divided, first into two, 

 then into three segments. By the middle of the week this 

 division is well marked, the terminal segments, i.e. the hands 

 and feet, forming broad flattened terminal plates, with free 

 rounded margins. A day or two later (Fig. 205), a distinction 

 appears in the hand, between a more swollen basal part, and a 

 thin flattened marginal part ; and towards the close of the week 

 the first traces of fingers appear, as small lobes at the boundary 

 between the basal and marginal portions, which soon extend ta 

 the free edge, but do not project beyond this until the sixth 

 week. 



