262 



Human Physiology. 



motion ; but its form is not clearly defined. By the fortieth 

 day, the shape of the fish is evident, the remains of the yolk 

 hang in a bag to its belly, but it soon becomes absorbed, and 

 then the fish is obliged to seek its own food, having exhausted 

 its embryonic provision. 



The condition of the fish about the thirtieth day is shown 

 in the embryo of the fowl as early as the eighth day Fig. 67, 



where the head forms more than 

 halt the animal, and the eye is 

 out of all proportion to the head. 

 The yolk is being absorbed 

 through a membrane and vessels, 

 which unite to form the umbi- 

 licus, the yolk of the egg being 

 to the embryo-chicken what the 

 placenta and blood of the mother 

 are to the human foetus. 



The appearance of the rudi- 

 mental spine in the mammal embryo at an early stage of 

 development is shown in Fig. 68, where the germ is seen, 

 shaped almost liked a grub or worm in the centre of the egg, 

 or matter from which it is to be organised 

 before the placenta is sufficiently devel- 

 oped for its nutriment. 



The inner membrane of the embryo 

 secretes the liquid in which it is suspended 

 during 'its fcetal life, protecting it from 

 injury by violence These waters escape 

 by the rupture of the membranes a little before birth. 



Fig. 67. EMBRYO FOWL OF 

 EIGHT DAYS.* 



Fig. 68. MAMMAL 

 OVUM. 



* A further advanced embryo, with an apparatus of nutrition, called the 

 allantois, a, with the umbilical vessels, b, branching over it. c. The exter- 

 nal ear. d. Cerebellum, f. Hemispheres. The eye is very large, and 

 far advanced ; the mouth begins to take the shape of a bill, and the legs 

 and wings are sprouting. 



