CHAP. IV.] THE SKELETON. 45 



open until the second year, and occasionally persists through- 

 out life. The base of the skull is much thicker and stronger 

 than the walls and roof ; it presents a 

 number of openings for the passage of 

 the cranial nerves, blood-vessels, etc. 



The diameters of the foetal skull 

 given by King are : 



Occipito-mental (from posterior fontanelle 



to chin) . . . . 5| inches (140 mm.). 



Occipito-frontal (centre of frontal bone to 



occiput) . . . . 4-1- inches (114 mm.). 



Bi-parietal (from one parietal prominence FlG 45 .Z T ' HE SKULL AT 



to another) . . 3J inches (89 mm.). BIRTH. Superior surface. 1, 



posterior fontanelle ; 2, sagit- 

 tal suture; 4, anterior fon- 



The foetal cranial bones being imper- taneiie; A, A, bi-parietai 



P ,-, -r* i i JT i -i diameter; B, B, bi-temporal 



fectly ossified, and their edges separated diameter. 



by membranous intervals, they are 



readily moulded, and they overlap one another more or less 



during parturition. 



The pelvic cavity. The pelvis, so called from its resemblance 

 to a basin, is stronger and more massively constructed than 

 either the cranial or the thoracic cavity. It is composed of 

 four bones, the ossa innominata, forming sides and front, and 

 the sacrum and coccyx, completing it behind. It is divided 

 by a brim or prominent line, the linea ilio-pectinea, into the 

 false and true pelvis. The false pelvis is all that expanded > 

 portion of the pelvis situated above the brim : it forms an in- 

 complete or " false " basin. The true pelvis is all that portion 

 situated below the brim. Its cavity is a little wider in every 

 direction than the brim itself, while the false pelvis is a great 

 deal wider. The brim is, therefore, a narrowed bony ring or 

 aperture between these two cavities; hence it is often termed 

 the "strait"; while the space included within the strait or 

 brim, is called the " inlet." The true bony pelvis is a basin 

 with incomplete walls of bone and without a bottom to it: the 

 opening below is called the "inferior strait" or "outlet." 



The female pelvis differs from that of the male in those 

 particulars which render it better adapted to parturition, 

 notably in being wider in every direction, which gives more 



