60 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 66. — The frontal bone seen from in front (i). 

 Fig. 67. — The frontal bone seen from behind (i). 



presents one-half of the sagittal groove, while the mastoid angle contains a small portion of the 

 sigmoid groove (see also Figs. 43 and 44). Digitate impressions and cerebral juga likewise occur 

 and granular foveolce granulates {Pacchionian depressions) are still more common. 



The parietal bone develops in membrane in the third fetal month from a center of ossification situated in the pari- 

 etal eminence. Even in the new-born the bony trabecular show a distinct radiation from this point. 



THE FRONTAL BONE. 



The frontal bone (Figs. 66 to 69) consists of a vertical arched portion and of a horizontal 

 portion. The vertical portion is known as the frontal portion and the horizontal portion is 

 composed of two orbital plates, and a small median nasal portion. At the orbital margins the 

 horizontal and vertical portions become continuous. 



The frontal portion, the main portion of the entire bone, articulates in the coronal suture 

 with both parietal bones by its parietal border (Figs. 39 and 40) and in the sphenofrontal suture 

 with the greater wing of the sphenoid bone. It forms the entire frontal portion of the cranial 

 vertex and presents two surfaces for examination, an external frontal surface and an internal 

 cerebral surface. 



The frontal surface (Fig. 66) is markedly convex in both the sagittal and the transverse 

 direction and presents some distance above the orbital cavities two feebly projecting flattened 

 elevations, the frontal eminences. Immediately above the orbital margins and parallel to them 

 are two slightly projecting ridges, the superciliary arches, the development of which varies con- 

 siderably in different individuals; the flat area between these two ridges is called the glabella. 

 The remainder of the external surface is smooth, although there may be a slight roughening 

 in the median line which represents the remains of the original frontal or metopic suture. 



The supraorbital border is situated at the junction of the vertical with the orbital plate. A 

 portion of it is furnished by the zygomatic process of the frontal bone, which also forms part of 

 the external orbital margin and, in the latter situation, articulates with the frontosphenoidal 

 process of the zygomatic bone in the zygomaticofrontal suture (Figs. 37 and 38). The temporal 

 line commences at the zygomatic process and separates the frontal surface of the frontal portion 

 of the bone from the small temporal surface, the latter surface, almost in the sagittal plane, 

 forming a portion of the planum temporalc and being that part of the frontal bone which borders 

 upon the temporal surface of the greater wing of the sphenoid bone. 



Immediately above the supraorbital border there are foramina, which may be represented 

 by notches of varying depth in the border itself. The inner one is designated as the frontal 

 notch or foramen (Fig. 65), while the outer one is known as the supraorbital notch or foramen* 

 (Figs. 66, 68, and 69). 



The inner or cerebral surface of the frontal portion (Fig. 67) presents a median ridge upon 



* The supraorbital notch is much more frequently present as a foramen than the frontal notch; sometimes both 

 of the notches form a single shallow groove. 



