366 



The Pelvis 



measured by the obstetrician in the occipito-frontal 

 diameter, ab, in the occipito-mental, om, in the cervico-bregmatic, //, 

 and in the fronto-mental diameter, bm. The fronto-mental measure- 

 ment is small in the fcetus, because the jaw presents no teeth and the 

 ramus hardly exists. 



Skull at birth, showing 

 lateral fontanelles : 



a l>, occipito-frontal dia- 

 meter. 



o in, occipito-mental. 



/' in, fronto-mental. 



1 1, cervico-bregmatic. 



The measurements of these diameters are thus given : a b, 4^ in., 

 om, 5 in., //, 3! in., bm, 3} in. of the male foetal head. Bregma (ftpcyfia) 

 means the ' top of the head ' ; in Latin the word is sinciput (semi, 

 caput}. 



In parturition the long diameter of the head enters the superior 

 plane in the transverse diameter ; passing through the middle plane, 

 it occupies the oblique diameter, and it emerges through the inferior 



Foetal head emerging 

 in ' first position ' ; 

 asterisk marks pre- 

 senting portion. 



plane antero-posteriorly, the occiput under the pubic arch and the 

 face to the coccyx. Thus in its progress through each plane the long 

 diameter of the head occupies the longest pelvic diameter. The 

 adjacent sketch shows the head escaping through the outlet, its long 



