332 



EMBRYOLOGY. 



having contracted adhesions with itself, forms an uninter- 

 rupted cyst or envelope for the entire contents of the egg, 



being everywhere in imme- 

 diate contact with the mem- 

 brane of the shell, from which 

 it must be peeled when they 

 are separated ; in the inte- 

 rior of the allantois, white 



\V~ * ~\_ X "" J / r~(* A\\ 



V; u ^<(vy f) i flocculent precipitates from 



the urine occur, and these 

 accumulate at length to such 

 an extent that they conceal 



,. , the embryo in a greater or 

 Fior. 355. Magnified view of the , , J mi n 



embrvo of the Lacerta ayilis, two less de g ree ' The allantois, 

 and a half lines in length, for con- as the complete fcetal enve- 

 trast with the other embryos figured : lope, is entitled the chorion. 

 a, corpora quadrigemina ; b, cleft of j n the brain, the corpora 

 the eye ; c olfactory depression ; d, quadri gemina, which have 

 branchial fissures already disappear- . & , , , , . , 



ing ; C , anterior extremity ; /, hinder remained very much behind 

 extremity; ff , tail. in development, are thrown 



backwards under the hemi- 

 spheres ; the pineal gland and cerebellum increase ; the latter 

 becomes marked with deep scissures. Over the eye, the eye- 

 lids grow till they meet, but without uniting ; the iris advances, 

 the cornea rises, the lenticular prominence remains, whilst the 

 lens recedes, and so the anterior chamber, which had hitherto 

 been wanting, is produced ; there is no appearance of pupillary 

 membrane. In the ear, the labyrinth becomes osseous at the 

 beginning of the third week. In the heart, the valvular sys- 

 tem is evolved ; the anterior arteries are detached more and 

 more from the descending aorta, and disappear altogether to- 

 wards the end of the period ; the pulmonary arteries become 

 much larger, and their terminations in the aorta have con- 

 tracted and become mere anastomosing channels ductus ar- 

 teriosi. The kidneys grow rapidly. The corpora Wolffiana 

 shrink continually, but in male embryos they may still be de- 

 tected as rudiments near the testes, even after the epoch of 

 foetal life is over. The right ovary, as has been stated, is ar- 

 rested in its growth, and is soon after birth completely absorbed ; 

 the right oviduct also disappears, although a trace of it may be 

 discovered in some birds at every period of their life. From 



