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child may be compared to a cone^ the apex of which presents itself 

 first. Of course, under these circumstances, the pressure upon the 

 child is constantly increasing as it descends, and the external parts 

 not having been thoroughly dilated, when the body is born and the 

 head engages, it is much more liable to prove fatal to the child in 

 consequence of the detention that almost unavoidably ensues ; the 

 prognosis^ therefore, in such cases is less favourable than in a simple 

 breech j^^^sejitation. — Diagnosis. Presentations of the feet may be 

 readily distinguished. Before the membranes have ruptured, the 

 bag of waters often protrudes in a more cylindrical form, or like the 

 finger of a glove, and we discover that the presenting part is smaller 

 than either the head or breech. At this stage we cannot readily dis- 

 tinguish whether it be the superior or inferior extremity that presents. 

 After the membranes have ruptured, the foot will be recognised by 

 its greater length, by the rounded instep, by the uniform length of 

 the toes, by the absence of a thumb, and by the presence of the 

 heel with the ankle bone on either side. The knee may be dis- 

 tinguished from the elbow, with which it is liable to be confounded, 

 from the fact, that it is thicker, that it has two prominences, and a 

 depression between them ; while the elbow, which is thinner, pre- 

 sents between the two prominences, a projection, in which it seems 

 to end. (Fig. 25.) 



