MECHANISM OF LABOUR. 59 



whatever. Hence the positions of the child, at the commencement of 

 labour, resolve themselves into two divisions, viz. : where the median 

 line of the child's body is parallel with that of the uterus, and where 

 it is not ; the first we shall call natural^ the seconA, faulty presen- 

 tations of the child." — Righy. 



Vertex presentations. — The vertex may present at the brim of the 

 pelvis in various positions ; some obstetrical writers enumerate as 

 many as eight, others only four, whilst a third class take the inter- 

 mediate number of six. The latter is the division of Baudelocque, 

 and the one most generally adopted in the schools. These are as 

 follows, enumerated in the order of their most frequent occurrence. 



1st. Vertex at the left acetabulum; Forehead at the right sacro-iliac junction. 



2d. " right " " left " 



3d. " symphysis pubis, " promontory of the sacrum. 



4th. '• right sacro-iliac junction, '* left acetabulum. 



5th. " left " " " right " 



6th. " promontory of sacrum, " symphysis pubis. 



Naegele and others make four, leaving out the fifth and sixth. 

 Rigby makes only two, viz., the first and second, whilst Ramsbotham, 

 Flamant, &c., make eight, adding to those already enumerated, 1st, 

 the face inclining to the right ilium, the occiput to the left, the right 

 ear behind the symphysis pubis, the left towards the spinal column. 

 2d, the reverse of the first, face to the left ilium, occiput to the right, 

 right ear towards the promontory of sacrum, left behind symphysis 

 pubis. The remaining six follow in the order given above. 



According to this table, the first three are called occipito-anterior, 

 the last three occijnto-posterior. 



In regard to i\\e frequency of these positions, it may be stated that 

 Naegele maintains that the fourth position of the vertex is much more 

 common than the second, and that the fifth and sixth are so rare that 

 they are discarded entirely by many eminent practitioners, they 

 having never met with them. 



Cranial presentations are by far the most numerous of the varie- 

 ties that offer themselves, and of these, those of the vertex in the 

 first position, occur most frequently. Madame Boivin states, that in 

 supervising twenty thousand five hundred and seventeen labours at 

 the Maternite Lying-in Hospital, at Paris, she found fifteen thousand 

 six hundred and ninety-three cases in which the vertex presented in 

 the first position. 



The greater frequency of vertex presentations may be readily 

 accounted for. It will be remembered that the fcetus hangs suspended 

 in the liquor amnii by the umbilical cord; which is attracted nearer 

 to its pelvic than cephalic extremity ; the head being the heaviest part, 

 consequently becomes the most dependent. 



Neither is it difficult to explain why the head in labour more com- 



