THE HEAD. :;:, 



jtoint win re tlic l>ono is bent posteriorly; they separate the anterior lateral 

 from the corresponding posterior lateral border, and are occupied by tho 

 tuberous portion of the temporal Ixme. 



Sti-utinrf. Tho occipital bone contiiins much spongy nubstain i . 



'"juni'Ht. It is developed from four centres of ossification : one, tho 

 anterior, is single, and forms tho occipital protuberance; another, tho 

 posterior, also single, forms the basilar process ; the other two are pairs, ;unl 

 comprise each a condylo, with the styloid process and tho corresponding 

 condyloid foramen. 



2. The Parietal Bone. 



The parietal is a wide and thin bone, very much arched to form the roof 

 of tho cranial cavity. It is bounded above by the occipital bone, below 

 by the frontal, and laterally by the two temporal bones. It otters for study 

 an t'j-t'-riiii! :m<l internal face, and a circumference divided into four regions or 



Face*. The external face is convex. It exhibits two curved ^ : 'lges whose 

 concavity is directed outwards ; these two crests, which ar' .ormed the 

 parietal ridges, approach each other and unite superiorly, tf ae continued 

 with the antero-posterior ridge of the occipital bone ; bel they diverge 

 and proceed, one on each side, to join the supraorbital process. They 

 divide the surface of the bone into three portions : two lateral, which are 

 rough and traversed by vascular channels, forming part of the temporal fossae; 

 the third, or middle, is plane, smooth, and of a triangular form, and covered 

 by the skin. The internal face is concave, covered by digital impressions, 

 and grooved by small vascular canals ; it offers, on the median line, and 

 altogether above, the parietal eminence. 1 This trifacial and very salient pro- 

 jection presents at its base, on each side, an excavation elongated trans- 

 versely, into which opens the parieto-temporal canal, and which is destined 

 to lodge a venous sinus. It is continued, in front, by a median crest, which 

 is often replaced by a slight groove, the saggital furrow, bordered by linear 

 imprints. Two other ridges, resulting from tho abutment of the lateral 

 border of the bone against the anterior face of the petrous bone, rise from the 

 sides of this eminence and descend to the sphenoid bone ; they separate the 

 .i-iil fmm tho cerebellar cavity. 



Borders. The superior border is notched, thick, and slightly dentated ; 

 it articulates with the occipital bone. The inferior border, slightly concave, 

 and deeply dentated, offers an external bevel in its middle portion, and an 

 internal bevel on its sides; it corresponds with the frontal bone. Tho 

 lnt> ml borders are very thin, and are cut at the expense of the external plate 

 into a wide, sloping edge, which shows a groove destined to form the 

 parieto temporal canal. A very prominent angle separates each into two 

 portions, an inferior, that articulates by suture with the squamous portion 

 of the temporal bone ; and a superior, curved inwards towards tho centre of 

 the cranial cavity; the hitter portion of the lateral border is in contact 

 with the anterior face of tho petrous portion of tho temporal bone, with 

 which it concurs to form the lateral crest that descends to tho parietal 

 eminence. 



Sfntrtnre. This bone contains much compact tissue, tho spongy Riiln 

 stance existing only in its middle. 



1>. It is developed from two large centres of ossification, to 



1 The intenml occipital eminent of Man. 



P 2 



