86 /'///: 



which is added a single centre to form the parietal eminence. 1 In < arly 

 life the parietal ridges arc absent. 



3. Frontal 



The frontal is a flat quadrilateral bone, whoso sides are bent in llu; 

 middle at an acute angle, and are carried buck, and a little inwards, in m< ( -t 

 tho wings of the sphenoid bone. It assists in funning tin- cranial mot' ami 

 part of the face. It is bordered : above, by the parietal bone ; below, by tho 

 nasal and lachrymal bones ; and on each side, by tho temporal bones. It 

 offers for study an external and an internal face, and fuur borders. 



Faces. The external face is divided, by tho double flexure of tho bone, 

 into three regions : a middle and two lateral. The first, nearly plane, is 

 lozenge-shaped, is covered by the skin, and constitutes tho base of the l'<>n-- 

 hcad. It gives rise on each side, at the point where it is inflected, to a lin^ 

 process, flattened above and below, which curves backward, forming the ori>il<il 

 arch. The superior or external face of this process is convex and slightly 

 roughened; tho internal face is smooth and concave, and forms part of tin; 

 orbital fossa. Its posterior border, thick and concave, is continued, in- 

 wardly, with tho corresponding parietal ridge, and outwardly with the 

 superior border of the zygoinatic process. It limits, in front, the temporal 

 fossa. The anterior border, also concave, but thin, concurs in tho forma- 

 tion of the orbital margin ; the summit, thickened and denticulated, rests 

 upon, and is united to, the zygomatic process of the temporal bone ; the base 

 is wide, and is traversed by an opening termed the supraorbital, or SIIJK /- 

 ciliary foramen. The two lateral regions of the external face of tho frontal 

 bone are slightly excavated, and assist, for the greater portion of their 

 extent, to form tho orbits. They often show, near the base of tho orbital 

 arch, a small depression corresponding to tho flexure described by tho 

 great oblique muscle of the eye in passing through its pulley. 



The internal face of the frontal bone is concave, and divided into two 

 unequal parts by a transverse ridge, corresponding to the anterior border of 

 the cribriform plate of the ethmoid bone. The superior, the most extensive, 

 is covered with digital impressions, and belongs to the cranial cavity. It 

 exhibits : 1, On the median line, a slight furrow, or a crest which is con- 

 tinuous, above, with the median ridge of the parietal bone, and below, with 

 the crista-yalli process ; 2, On the sides, and in the re-entering angle formed 

 by tho flexure of the bone, there is a narrow slit, or mortice, which receives 

 the wing of tho sphenoid bone. Tho inferior part is united, on tho median 

 line, to tho perpendicular plate of the ethmoid. It assists in forming the 

 bottom of the nasal cavities, and presents laterally two large openiiiL's 

 which lead to tho frontal sinuses vast anfractuous spaces excavated 

 between the two plates of the bone. 



Borders. Tho superior border is denticulated, and cut obliquely, in its 

 middle portion, at tho expense of tho internal plate, ami on the lateral parts 

 at the expense of the external table ; it is in contact with tho parietal and 



1 Tli : s centre is desciibed as the interparietal loin 1 hy those anatomists who consider 

 the two lateral .utr. .- as two di.-tinH parietal. (I.eyh is one of the vi terinaiy aii;it..mi.-ts 

 who ili .-<-iii> tliis nucleus ns a separate done, designating it the /afrfform or faferpoffotal 

 bone. He also describes the parietal as a jinir or douUe l><>ne ; when a- tin- majority of 

 Freueh anatomists ine]iid: the inteipant tal l' .,! ill m protuberance of tho 



pniietnl, which tlicy look ii|H>nas a nin^lr or impair l>one. I'crcivall names it a pair Ixme, 

 but follows tlie example of the Kivneh hippotoiiii-t- with regard to the int'Tparictal.) 



