THE STRUCTURE OF THE HUMAN SKULL. 12o 



squamous part, which bounds the posterior segment of the 

 foramen, is known as the Supra-occipital (So, So). All these 

 bones, eventually becoming anchylosed together, form the 

 occipital bone of the human anatomist ; or what we may term 

 the first, posterior, or Occipital segment of the skull. 



From the sides of the basi-sphenoid, external to the lingulm, 

 two wide processes, well-known as the "greater wings of the 

 sphenoid ' : or AUsphenoids (AS) spring, and unite sutnrally 

 with the expanded Parietal bones (Pa), which form the dome- 

 like crown of the skull, and unite in the middle line in the 

 sagittal suture. In this way a second, middle, or Parietal 

 segment of the skull is distinguishable. 



In like manner, the presphenoid passes, on each side, into 

 the smaller processes, the "lesser wings of the sphenoid," 

 alee minores, or wings of Ingrassias ; which, on account of their 

 relations to the orbits, have been well named the Orbito- 

 splienoids (OS). And these, externally and anteriorly, unite by 

 suture with the arched and expanded Frontal bones (Fr), 

 originally double, and separated by a median frontal suture, 

 which ordinarily early disappears. These bones not only meet 

 in front, but send in processes which roof over the orbits and 

 unite with the free anterior edges of the orbito-sphenoids, thus 

 leaving only a long and narrow vacuity, on each side of the 

 crista galli, and in front of the presphenoid. 



The presphenoid, the orbito-sphenoid, and the frontals are 

 the constituents of the third, anterior, or Frontal segment of the 

 skull. 



It will be observed, however, that this enumeration of the 

 bones of the three great segments of the skull does not account 

 for all the distinct osseous elements, which enter, directly and 

 indirectly, into its boundaries. If all the bones mentioned 

 are put together, there still remain four considerable vacuities ; 

 two small, already mentioned, in the proper front wall of the 

 skull, on each side of the crista galli; and one on each side, 

 posteriorly, between the occipital and parietal segments, of 

 very much larger size, and extremely irregular form. The 

 anterior vacuities are filled up by those spongy osseous masses, 

 united with the laiui na perpendicular is in the adult skull, which 



