B. ABNORMALITIES IN THE DEVELOPMENT, 

 OR DISEASES OF THE FETUS. 



a. Excess of Volume of the Fetus. 



Excess in the volume of the fetus is a comparative term. It 

 is the relation existing between the size of the fetus and the di- 

 mensions of the birth canal of th emother, rather than definite 

 abnormality in volume. Such comparative excess in size is not 

 rare in domestic animals, and is frequently a more or less serious 

 obstacle to the expulsion of the fetus. 



The causes of this comparative excess in fetal volume are 

 not clear. The excess maj^ be confined to one part of the body, 

 or may apply to the entire body. 



Prolonged gestation is sometimes believed to increase the 

 volume of the fetus. In the cow and mare there are great 

 variations in the duration of gestation, ranging from 30 to 90 

 days or even more. During this period the fetus is presumably 

 constantl}^ growing, and, if carried for 30 to 60 days bej'ond the 

 briefest duration of pregnancy, it would be but reasonable to ex- 

 pect that it may be larger because of this longer period of intra- 

 uterine development. 



Nev^ertheless it has not been possible to verify this suggestion 

 by clinical observation. Prolonged gestation does not commonly 

 result in such a growth of the fetus as to cause any serious ob- 

 stacle to its deliver}'. It is true that those fetuses which are 

 born after a comparatively short duration of gestation, prema- 

 ture births, are usually very small, but they are also correspond- 

 ingly immature. When they reach the average duration of 

 intra-uterine development they seem to be as large as though 

 carried for a much greater length of time. In one instance 

 which we noted, where the duration of gestation in a mare ex- 

 ceeded 12 months, the foal to which she gave birth was a pigmy 

 about half the size which would naturally have been expected 

 in harmony with the size of the sire and dam. 



Neuman (B. T. W., 1909, p. 702) records delivering a cow, 413 



days pregnant, of a putrid, emphysematous calf, weight 110 lbs. 



long hair, female, form of male. The impression is given 



that the large size was due to prolonged gestation. The fact 



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