Io8 OBSTETRICAL PHYSIOLOGY. 



Second Period. — In the third and fourth weeks of gestation in the Mare, 

 Ruminants, and Pig ; the third week in Carnivora ; there appear the 

 first traces of the embryo, and the head, body, and limbs can be distin- 

 guished. Towards the twenty-eighth day, the embryo of the Mare meas- 

 ures about six lines, and that of the Cow four lines ; that of the Sheep 

 at twenty-five days is four and a half lines ; and the Bitch at eighteen 

 days two lines. 



Third Period. — This is from the fifth to the eighth week with th^ Mare 

 and Cow ; the fifth to the seventh with the Sheep and Goat ; and the 

 fourth to the sixth with the Pig. The embryo of the Mare has acquired 

 a length of rather more than 2 inches ; that of the Cow i^ inches ; that 

 of the Sheep and Goat i^^ inches ; that of the Pig i^ inches; and 

 that of the Bitch 11 to 12 lines. 



Fourth Period. — This is from the ninth to the thirteenth week with the 

 Mare ; the ninth to the twelfth with the Cow ; the seventh to the eighth 

 and ninth with the Sheep and Goat ; the sixth to the eighth with the 

 Pig ; and the fifth week with Carnivora. The length of the fcetus of the 

 Mare is 6 inches; that of the Cow 5^^ inches ; that of the small Rumi- 

 nants 3^1^ inches ; that of the Pig 3 inches ; and that of the Dog 2j^ 

 inches. 



Fifth Period. — This extends from the fourteenth to the twenty-second 

 week in the Mare ; the thirteenth to the twentieth in the Cow; the tenth 

 to the thirteenth in the Sheep and Goat ; the eighth to the tenth in the 

 Pig; and the sixth week in Carnivora. At this stage the foetus of the 

 Mare is about 13 inches long ; that of the Cow 12 inches ; that of the 

 Sheep and Goat 6 inches ; that of the Pig 5 inches ; and that of the 

 Bitch 3^ inches. 



Sixth Period. — From the twenty-third to the thirty-fourth week in the 

 Mare ; the twenty-first to the thirty-second in the Cow ; the thirteenth 

 to the eighteenth in the Sheep and Goat ; the eleventh to the fifteenth 

 in the Pig ; the seventh to the eighth in Carnivora. The fcetus of the 

 Mare in this period has acquired a length of more than 2 feet ; that of 

 the Cow is about the same dimensions ; the fcetus of the Sheep is more 

 than a foot ; that of the Pig about 7 inches ; and that of the Bitch 5 

 inches. 



Seventh Period. — From the thirty-fifth to the forty-eighth week — up to 

 parturition, in the Mare ; the thirty-third to the fortieth in the Cow ; the 

 nineteenth to the twenty-first in the Sheep and Goat ; the fifteenth to 

 the seventeenth in the Pig ; the ninth week in the Bitch ; and the eighth 

 in the Cat. 



A newly-born foal measures about 3^ feet long ; a calf 2 feet ; a lamb 

 i^ feet ; a pig about 9 or 10 inches ; a puppy 6 to 8 inches ; and a 

 kitten about 5 inches. 



In this study of the evolution of the young animal in utero, one cannot 

 fail to be struck with the slowness with which development progresses 

 for a certain period, and its rapidity afterwards. The slowness in growth 

 may be accounted for by the extreme minuteness of the ovum at the 

 moment of impregnation, and its containing within itself alone the ele- 

 ments upon which the primary steps of evolution depend, there being at 

 first no direct connection between the embryo and the uterine vessels. 

 The parts which in reality grow most rapidly in the early period of ges- 

 tation, are the enveloping membranes and the fluids they contain. In 



