562 EMBRYOLOGY. 



1 inch ; at 24 days, \ to inch. The umbilical vesicle has 

 reached its maximum size. 



(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. 



(a.) Horse. The horse's embryo, at 6 weeks, has a length of 

 1-| inch ; at 7 weeks, 2 inches ; and at 8 weeks, 2f inches ; the 

 thoracic and abdominal cavities are closed. 



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

 corresponds to the 22-23 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 2f in length. 



(c.) Sheep. At the 5th 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, 2i inches. 



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

 about -f 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 If inch in length ; all organs are more or 

 less distinctly marked. 



IV. Period. Includes, in the horse, the 9th to the 13th 

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

 week ; in carnivora, the 5th week. 



