438 THE HUMAN SPECIES 



according to the position of the foetus, one or more extremity 

 may lie on the os uteri, or one of the upper extremities may 

 prolapse. 



It is characteristic of human transverse presentations that they 

 do not arise during labour, but are due to various antecedent 

 causes, and that in small and badly developed or macerated 

 foetuses, the malposition corrects itself, while in all other cases 

 version is possible. The conditions in the case of domestic 

 animals are very different. The transverse position arises 

 during, and as the result of, labour, and is developed from some 

 other position. It is commoner in horses than cattle. The 

 young lie transversely, with the back strongly bent and with one 

 end of the body lower than the other, so that either the back or 

 the belly is turned towards the inlet of the pelvis. Version is 

 possible in small animals, if the size of the genital canal permits ; 

 in larger animals version is only possible when one half of the 

 foetus has been torn away. Oblique positions only differ from 

 transverse positions in degree, and are only met with in the 

 human subject. The long axis of the child's trunk forms an 

 acute angle with the long diameter of the uterus, so that ob- 

 viously either the head or the breech must lie close to the os 

 uteri. This circumstance renders the oblique position more 

 favourable than the transverse. 



But whereas the oblique position is peculiar to human beings, 

 an abnormal position is observed in animals which can never 

 occur in man owing to the upright posture. This is the vertical 

 position of the foetus, in which one end lies against the mother's 

 belly and the other against her sacrum or lumbar vertebrae, so 

 that it sits or stands in the uterus with either its back or its 

 belly opposite the pelvic inlet. 



Considerable differences may thus be demonstrated between 

 the various factors tending to obstruct labour in human beings 

 and those found in animals. The most important difference, 

 however, still remains to be described, viz., the influence of the 

 pelvis on the course of parturition. As regards this, the domes- 

 tic animals in which the course of parturition can be observed 

 are much more suitably framed from an anatomical point of 

 view than the human female. Not only is the pelvis in animals 

 wide and roomy, but its component parts are more movable 



