116 OBSTETRICAL PHYSIOLOGY. 



foetus as a whole, it may be advisable to adopt the plan of dividing this 

 bodily development into periods, which will also give an approximate 

 idea of its age. From conception to maturity, utero-gestation may 

 therefore be divided into seven periods or stages, as follows : — 



First Period. — Towards the second week after conception, the ovum 

 or germ has passed from the ovary into the uterus ; it is then about a 

 line in diameter (one-twelfth of an inch). 



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

 Mare, Eurainants, and Pig ; the third week in Carnivora ; there appear 

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

 distinguished. Towards the twenty-eighth day, the embryo of the Mare 

 measures 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 the 

 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 If 

 inch ; that of the Sheep and Goat 1| inch ; that of the Pig If inch ; 

 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 foetus 

 of the Mare is 6 inches ; that of the Cow bh inches ; that of the small 

 Euminants 3J inches ; that of the Pig 3 inches ; and that of the Dog 

 2| 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 tentli 

 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 3i 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 foetus 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 foetus of the Sheep is more than 

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



Seventli 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 in the Bitch ; and the eighth 

 in the Cat. 



A newly-born Foal measures about 3i feet long ; a Calf 2 feet ; a 

 Lamb 1^ foot ; 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 pro- 

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

 in growth may be accounted for by the extreme minuteness of the ovum 



