462 



FOETAL DYSTOKIA. 

 Hock Peesentation. 



The mechanism of hock presentations is supposed to be as 

 follows: — The foetus, in the posterior presentation, lumbo-sacral 

 position, and impelled by the uterine contractions towards the cervix. 



Fig. 139. 

 Hock Presentation : Calf. 



reaches the inlet with the hind-limbs not quite extended, nor the axis 

 of the young creature quite coinciding, perhaps, with that of the passage. 

 Consequently, the legs come in contact with the pelvic brim below by 



Fig. 140. 

 Diagrams of the Hind-Limbs in Hock Presentation. 



the posterior surface of the shank, while the croup encounters the 

 sacro-vertebral angle above. 



The labour-pains continuing, the croup has a tendency to descend, 

 and, with the points of the hocks, to advance through the os: the latter 



