562 EMBRYOLOGY. 



{e.) Carnivora. — The villi appear on the chorion, and become 

 attached to the mucous membrane of the uterus. At 18 

 days, the embryo of the dog has a length of about ^ inch ; the 

 primitive groove and chorda dorsalis are present. At 19 or 20 

 days, the heart is present as an S-shaped tube ; the intestine 

 begins to form. At 21 days, indication of the eyes, ears, and, 

 "Wolffian body are present ; the limbs are present as small 

 blunt processes. 



III. Period. — Includes, in the horse and ox, the 5th to the 

 8th week ; in the sheep and gOat, the 5th, 6th, and first half of 

 the 7th week ; in the pig, the last half of the 4th, the 5th, and 

 first half of the 6th week ; in carnivora, the 4th week. 



{«.) Hors". — The horse's embryo^ at 6 weeks, has a length of 

 1|- incii. At 7 weeks, 2 inches; and at 8 weeks, 2|- inches; the 

 thoracic and abdominal cavities are closed. 



(6.) Ox. — At 6 weeks, the embryo is ^ inch in length, and 

 corresponds to the 22-2 o days-old dog's embryo. At 7 weeks, 

 it is about 1^ inch in length; the udder begins to form ; the 

 kidneys and ureters are present. At 8 weeks, the embryo is from 

 2 inches to 2|- in length. 



(c.) Sheep. — At the 5 th week, the embryo has a length of 

 1 inch, and, in development, corresponds to the 25 days-old 

 dog's embryo, 



(d.) Pig. — At 28 days, the embryo has a length of 1 inch. 

 At 37 days, 2-1 inches. 



(e.) Carnivora. — At 22-23 days, the embryo has a length of 

 about "I inch ; mouth-groove, nostrils, lungs, trachea, and larynx 

 are present ; the anus is still closed ; Wolffian body well formed ; 

 •limbs about one line in length. At 25 days, the thorax is closed, 

 and the abdominal cavity almost closed. At 26-28 days, the 

 embryo is about 1|^ inch in length ; all organs are more or 

 less distinctly marked. 



IV. Period. — Includes, in the horse, the 9th to the IStb 

 week; in cattle, the 9th to the 12th week; in the sheep and 

 goat, the last half of the 7th, the 8th, and the 9th weeks; in 

 pigs, the last half of the 6 th, the 7th, and first half of the 8th 

 week ; in carnivora, the 5 th week. 



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

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



