372 



WHALES 



Figure 20/. Right view of abdominal cavity of a 4-foot porpoise which drowned while giving 

 birth in a shrimpers' net {Texel, 7 July 1955). Note the position of the foetus in the vagina 

 and the left uterine horn, the top of which has become emptied. 



In the foregound: the right uterine horn and ovary. Above the foetus'' s tail the pelvic bone 

 and cervix can be seen clearly. The hatched line right of the cervix indicates the spot where the 

 embryonic membranes are torn. {Slijper, 1936.) 



is forced towards the cervix, i.e. the calf is born tail first, as, indeed, 

 observations show it is. 



From investigations of pregnant Cetaceans it has, however, appeared 

 that in some the final position is taken up very shortly before birth, and 

 that some foetuses face the cervix during most of the period of pregnancy. 

 Possibly, the situation changes quite a few times during pregnancy, and, 

 in any case, even if dissections reveal that the foetus faces the genital slit, 

 the tail may nevertheless emerge first, since, as Fig. 207 and 208 show, the 

 top of the uterine horn is attached to the abdominal wall close to the 

 pelvis. As the foetus becomes larger, the uterus therefore slumps forward 

 and causes the foetus to curve and sometimes even to double up. Towards 

 the end of pregnancy, however, the snout is almost always at the top of 

 the uterine horn, while the tail lies close to the cervix (Fig. 209). Sleptsov 

 (1940) found this position in most of the 635 pregnant dolphins and 

 Belugas mentioned earlier. The observations of W. van Ubrecht have 

 shown that in Fin Whales tail positions become more frequent as the 

 period of gestation advances. In the course of two months he found tail 

 positions only. My colleague, R. G. Chittleborough, who investigated 

 many Humpbacks in an advanced stage of pregnancy, also discovered a 

 clear preponderance of tail positions. 



