THE TEMPORAL BONES 39 



the anterior transmits the nasal nerve from the orbit and 

 anterior ethmoidal vessels; the posterior transmits the pos- 

 terior ethmoidal vessels. The frontal sinus opens at the root 

 of the nasal process. It is between the outer and inner tables, 

 over the root of the nose and divided by a bony septum. Out- 

 side and behind the orbital surface is a rough triangular area 

 for articulation with the great wing of the sphenoid. 



Cerebral Surface. This forms a large concavity for the 

 anterior lobes of the cerebrum. The orbital plates are convex 

 and marked by ridges and depressions, and are so thin as to 

 be transparent; these plates make an angle of about 60 degrees 

 with the upper part of the bone. From the upper margin 

 descends the frontal sulcus, running into the frontal crest at 

 the lower margin. At the base of the crest is usually a groove 

 converted into the foramen caecum by the approximation of 

 the ethmoid; this is usually open in children, but blind in adults. 

 The sides of this surface present grooves for the meningeal 

 vessels. The thin transverse edge bounding the surface behind 

 articulates with the greater and lesser wings of the sphenoid. 



The border of the vertical portion is thick, strongly serrated, 

 bevelled at the expense of the internal table above, where it 

 rests upon the parietal bones, and at the expense of the external 

 table at each side, where it receives the lateral pressure of 

 those bones; this border is continued below into a triangular 

 rough surface which articulates with the great wing of the 

 sphenoid. The posterior border of the horizontal portion is thin, 

 serrated, and articulates with the lesser wing of the sphenoid. 



The Temporal Bones 



The temporal bone (tempus, time, as hair first becomes gray 

 in this region, indicating age) helps form the side and base of 

 the skull and contains the organ of hearing. It presents three 

 parts the squamous, mastoid, and pyramidal, which includes 

 the petrous and tympanic. It articulates with five bones 

 posteriorly and internally with the occipital, above with the 

 parietal, in front with the sphenoid and malar, and below 

 with the inferior maxilla. 



The squamous portion (scale) presents a vertical portion 

 and a narrow horizontal portion at the base of the skull. It 

 is limited above by an arched border describing two-thirds 



