Foetal Head 365 



Thus, at the brim the longest diameter is the transverse, the 

 shortest is the antero-posterior. In the middle plane the oblique dia- 

 meter is the longest, and the shortest is the antero-posterior. At the 

 outlet the antero-posterior is the longest and the transverse the shortest 



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Axes. A line, ed, drawn at right angles to the middle of the superior 

 plane shows the axis of inlet ; it extends between the navel and the tip 

 of the coccyx ; the axis of outlet passes from the sacro-vertebral angle 

 through the anus. 



The spine of the ischium greatly influences the direction of the foetal 

 head during parturition. 



The foetal head. Though the base of the foetal skull is solidly 

 ped, to protect important nerves and ganglia, the vault is ex- 

 tremely compressible, the edges of the bones being bevelled, and con- 

 nected by membranous seams, so as to permit overlapping as the head 

 passes through the pelvic straits. 



Where three or more sutures meet, the membranous seams are wide 

 and conspicuous, and the arterial pulsation which there exists gives 

 those areas the name of font ane lie*. There is a fontanelle at each 

 angle of the parietal bone, those in the middle of the coronal and 

 lambdoid sutures being extremely important ; by their shape and posi- 

 tion the finger of the obstetrician recognises the kind of head presenta- 

 tion with which he is dealing. (See fig. on p. 366.) 



The anterior fontanelle is Kke the ace of diamonds ; the posterior 

 is triangular. The anterior is wide, but the posterior is encroached 

 upon by the close proximity of the corners of the three bones which 

 bound it In the case of chronic hydrocephalus the anterior fontanelle 

 may not be closed until after puberty. The lateral halves of the frontal 

 bone are connected by a loose suture which extends downwards from 

 the front of the anterior fontanelle ; it is the continuation of the sagitta 



