Development of the Mammal 325 



For example, an embryo with a crown-rump 

 length of 1 6 mm. would be about forty days 

 old. This formula may be employed until a 

 length of TOO mm. is reached ; from 100 mm. 

 to 2 20 mm. the length in millimeters equals the 

 age in days. 



ABNORMALITIES IN HUMAN DEVELOPMENT 



Attention will here be called to some of the 

 more common abnormalities in the develop- 

 ment of man, but for more detailed information 

 upon this subject the reader is referred to 

 treatises upon teretology and obstetrics. 



Abnormalities occur in connection with both 

 the foetal membranes and the foetus proper. 

 Of the former group two or three will be men- 

 tioned. Amniotic abnormalities may consist 

 in a deficiency or an excess of fluid. The 

 normal amount is one to two pints at term. 

 A deficiency may cause fcetal abnormalities 

 through adhesions ; while an excess, which 

 sometimes reaches five or six gallons, may also 

 cause abnormalities or premature birth. Am- 

 niotic bands, caused by the pulling out into 

 bands of adhesions between the amnion and 

 fcetus, may produce deformities or death. 



The umbilical cord, which is usually about 



