DEVELOPMENT OF THE FCETUS, 563 



(a.) Horse. — At the 9th week, the embryo measures 3i inches ; 

 the external ears are very small ; the Wolffian body, genital 

 glands, kidneys, and suprarenal capsules are present. At 10 

 weeks, the embryo measures 3i inches ; the internal and 

 external genital organs are formed. At 11 weeks, the embryo 

 measures 4i- inches ; at 12 weeks, 4f inches; and at 13 Aveeks, 

 of inches. 



(6.) Ox. — At 9 weeks, the embryo measures almost 3t inches. 

 At 10 weeks, 3f inches. At 11 weeks, 4f inches, and its 

 development corresponds to that of the horse's embryo of the 

 same age ; mouth-groove and nostrils are closed by a thin mem- 

 brane ; the divisions of the stomach are present. At 12 weeks, 

 the embryo measures 5f inches. 



(c.) Sheep and Goat. — At 8 weeks, the length of the embryo 

 is about 2 inches. At 9 weeks, 3f inches ; the nostrils are still 

 closed. 



(d.) Pig. — Length of embryo in the 8th week is 3i inches. 



(e.) Garnivora. — Length of embryo in the 5th week is 2f 

 inches. 



V. Period. — Includes, in the horse, the 14th to the 22nd 

 week ; in the ox, the 13th to the 20th ; in the sheep and goat, 

 the 10th to the 13th; in the pig, the last half of the 8th, the 

 9th, and the 10th week ; in carnivora, the 6th week. 



{a.) Horse. — During this period the embryo increases from 

 5f inches to 14f inches. At 17 weeks, the first hair appears on 

 the lips. At 22 weeks, the lips, eyelids, and point of tail are 

 provided with hair. 



(6.) Ox. — The embryo increases from 5f inches to 12f. At 

 18 weeks, the hair appears, and the testicles descend into the 

 scrotum. 



(c.) Sheefy and Goat — At the end of this period the embryo 

 measured 6f inches ; hair is still wanting. 



(d.) Pig. — The embryo measures 5j inches. 



(e.) Carnivora. — The embryo has a length of S\ inches. 



VI. Period. — Includes, in the horse, the 23rd to the 34th 

 week ; in cattle, the 21st to the 82nd week ; in the sheep and 

 goat, from the last half of the 13th to the 18th week ; in the 

 pig, from the 11th to the first half of the 15th ; in the dog, the 

 7th and 8th weeks ; in the cat, to the end of the 7th week. 



