go HUMAN EMBRYO AND FETAL MEMBRANES 



The following are the estimated ages and lengths of human embryos, 

 according to Mall, and their weights according to Jackson. 



Crown-rump length Crown-heel length Weight 

 Age (CR), or sitting (CH), or standing in 



height (mm.)- height (mm.). grams 



Twenty-one days 0.5 0.5 



Twenty-eight days 2.5 2.5 



Thirty-five days 5.5 5-5 4 



Forty-two days n.o u.o 



Forty-nine days 17.0 19.0 



Second lunar month 25.0 30.0 . 3 



Third lunar month 68. o 98.0 36 



Fourth lunar month 121.0 180.0 120 



Fifth lunar month 167.0 250.0 330 



Sixth lunar month 210.0 3!5- 635 



Seventh lunar month 245.0 370.0 1220 



Eighth lunar month. 284.0 425.0 1700 



Ninth lunar month 316.0 470.0 2240 



Tenth lunar month 345 . o 500 . o 3200 



For comparison and reference the gestation periods of a few representative mammals 

 are appended: 



Opossum 13 days Pig 17 weeks 



Mouse 20 days 



Rat 21 days 



Sheep 21 weeks 



Cow 41 weeks 



Rabbit 30 days Horse 48 weeks 



Cat 8 weeks Rhinoceros. . . 18 months 



Dog, guinea pig 9 weeks 



Elephant 20 months 



