ORGANS OF GENERATION. 



19 



of a quadrangular shape ; it is formed by the rounding off of the 

 four corners of the two frontal and the two parietal bones. The 

 posterior is triangular, and formed by the union of three bones, the 

 superior posterior angles of the two parietal, and the upper angle 

 of the occipital. A knowledge of these fontanelles is of great im- 

 portance in the practice of midwifery, as they are the chief means 

 of diagnosticating the position of the child's head in labour. The 

 great advantage gained fromi this arrangement of the child's head, is 

 that it allows a more uniform growth and development to the brain 

 than could have taken place had the cranium been solid, and what 

 is perhaps of greater importance, it allows the bones to overlap, and 

 thus permits a certain amount of compression, which enables the 

 head to be pushed through a smaller space thaJ%,if it had been 

 formed of one continuous piece. * 



The dimensions of the foetal head have been variously stated by 

 obstetrical writers, each basing his report upon the result of his own 

 observations. The following table, modified from Churchill's, is the 

 best average. 



The longitudinal or occipito-frontal diameter, Fig 



6, (' ^) is from .... 



The transverse or bi-parietal, from one parietal 



boss to the opposite, . 

 The occipito mental, or oblique, (^ ^) 

 The cervico-bregmatic, C ^) . 

 The trachelo-bregmatic, . 

 The inter-auricular, 

 The bi malar, 

 The fronto-mentnl, (' 8) 

 The transverse diameter of the shoulders, 



hips, . 



In general, it may be observed that all the measurements are 

 male than in 



Fig. 6. 



larger in the 

 female children. 



Regions of the head. — Vertex. 

 A circle of an inch in radius 

 around the posterior fontanelle 

 as a centre. Top of the head. 

 — Sometimes called the breg- 

 matic region ; besides which 

 the terms lateral^ chin, face, 

 forehead, base, are used to de- 

 fiine different regions of the 

 head which may present. By 

 the base is understood all the 

 immovable parts of it, viz. : 

 the sphenoid in the centre, the 

 temporal bones laterally, to- 

 gether with the bones of the face 



