254 NORMAL PARTURITION. 



against the branches of the ilium. Entrance into the inlet must there- 

 fore be slow, difficult, and painful for the mother, and when this 

 first obstacle is overcome and the croup is in the pelvic cavity, the chest 

 has to follow, and to submit to the same compression at the inlet as in 

 the anterior presentation. But this part of the fcetus is much less 

 favourably disposed for such a reduction of dimensions in this position ; 

 as the resistance offered by the walls of the maternal pelvis has a ten- 

 dency to erect the dorsal spines, and to carry the ribs and sternum 

 forward — all this going to increase the diameter of the fcetus in every 

 direction. It is only, then, by direct compression or squeezing, that 

 the necessary diminution in the diameters of the young creature can be 

 effected, and not by a kind of physiological decrease, as in the anterior 

 pi'esentation. 



There is also the obstacle offered by the hair of the foetus, the " set " 

 of which is against the direction of movement ; and this obstacle will 

 be greatly increased if the fluids have escaped for some time, and the 

 parts are more or less dry. 



Taking all these considerations into account, it will be seen that in 

 this position, even when birth is possible with extraneous assistance, 

 labour must be long and exhausting, and that the young creature 

 incurs the greatest danger. Labour, however, is more likely to be 

 successful and less tedious if the haunches of the foetus present one 

 after the other at the inlet ; so that a slight obliquity in the presenta- 

 tion makes a great difference ; and it is just possible that when birth 

 takes place in this position without aid, this obliquity may have been 

 present. 



Cow. 



Anterior Presentation. 



Mechanism of Partiirition in the Dorso-sacral Position. — In the Cow, 

 the mechanism of parturition in this presentation is similar to that in 

 the Mare. Saint-Cyr shows, from actual measurements of Cow and 

 foetus, that the head of the Calf can easily pass into the inlet, owing to 

 its less diameter, and that the principal difficulty is encountered by the 

 foetal thorax, which is slightly larger in every sense than the inlet. ^ 



The bicoxo-femoral diameter of the croup slightly exceeds the bis- 

 iliac diameter of the pelvis ; but it is possible that the pelvis of the 

 Calf, being more cartilaginous and supple than that of the Foal, may 

 be submitted to a slight temporary compression. It is to be remarked, 

 however, that the progress of the Calf through the pelvis must be more 

 protracted tban that of the Foal, owing to the greater length of the 

 maternal pubic symphysis, and the more considerable extent of the 

 pelvic walls, as well as the peculiar curve in the floor of the pelvis ; 

 though these disadvantages are somewhat compensated for by the greater 

 mobility of the sacrum. And, as we have seen, such is really the 

 case, the duration of parturition being shorter in the Mare than in 

 the Cow.-' 



The other positions in this presentation do not differ much from 



1 Saint-Cjr in these observations measured the thorax after the birth of the young 

 creatures, and when the lungs had become expanded. He does not appear to have made 

 any allowance for this expansion, which of course makes a difference in the size of the 

 thorax after biith. 



- The fact that parturition is more quickly pei formed in the Mare than any other 

 quadruped was well known to Aristotle : Equa, omnium qiiadrupedem, J'acilllme, parit. 



