46 



THE SKELETUX 



Articulations. — The parietal articulates with its fellow, the occipital, squa- 

 mosal frontal, si)henoid, and the epipteric bones when present. Occasionally the 

 squamosal and epipteric may exclude the parietal from union with the greater wing 

 of the si)henoid. 



Blood-supply. — From the middle meningeal, occipital, and supraorbital 

 arteries. 



Ossification. — The parietal ossifies from an earthy si)ot deposited in the outer 

 layer of the meml^ranous wall of the skull about the seventh week. This bone is 

 sometimes divided bv a horizontal suture. 



THE FRONTAL 



This bone bears much the same relation to the anterior part of the skull that 

 the occipital bears to the posterior. It has, not inaptly, been compared to a cockle 

 shell. The inner or posterior surface is concave, forming a deep fossa for the 



Fig. 56. — The Fkontal. (Anterior view.) 



TEMPORAL RIDGE 



SUPRAORBITAL NOTCH 

 __ EXTERNAL ANGUUR 

 PROCESS 



recei)tion of the frontal lobes of the cerebrum. There is a gap in tlie lower part of 

 the hone known as the ethmoidal notch, which overlaps by its thin edges the 

 cribriform plate of the ethmoid and forms, with that bone, the internal orifices of 

 the anterior and posterior ethmoidal canals. The anterior part of this notch 

 articulates Avith the crista galli, and the small hole in the line of suture is the 

 foramen caecum. Prolonged vertically upwards from the point of union with the 

 crista is a ridge of bone, which gradually opens out to form a furrow for the 

 reception of the superior longitudinal sinus; the ridge serves for the attachment of 

 the anterior ])art of the falx cerel)ri. The thin lamina? of bone on each side of tlie 

 ethmcjidal notcli are termed orbital plates, because they form the greater j)art of 

 the roof of each orbit. As a rule, they present deep depressions for the convo- 

 lutions on the orbital surface of the cerebrum. The rest of the cerebral surface of 

 the frontal is fairly smooth, and presents a few furrows for meningeal arteries, and, 

 near the median groove, pits for Pacchionian bodies. 



The external surface is convex and smooth, often divided by an imperfect 



