TEMPORAL BONES. 



143 



one another by a thin bony septum. They give rise to the prominences above 

 the root of the nose, called the nasal eminences and superciliary ridges. In the 

 child they are generally absent, and they become gradually developed as age 

 advances. These cavities vary in size in different persons, are larger in men 

 than in women, and are frequently of unequal size on the two sides, the left 

 being commonly the larger. Occasionally they are subdivided by incomplete 

 bony laminae. They are lined by mucous membrane, and communicate with 

 the nose by the infundibulum, and occasionally with each other by apertures 

 in their septum. 



The Internal Surface of the Horizontal Portion presents the convex upper 

 surfaces of the orbital plates, separated from each other in the middle line by 

 the ethmoidal notch, and marked by eminences and depressions for the con- 

 volutions of the anterior lobes of the brain. 



Borders. 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 border of the horizontal portion is thin, serrated, and articu- 

 lates with the lesser wing of the sphenoid. 



Structure. The vertical portion and external angular processes are very 

 thick, consisting of diploic tissue contained between two compact laminae. 

 The horizontal portion is thin r translucent, and composed entirely of compact 

 tissue ; hence the facility with which instruments can penetrate the cranium 

 through this part of the orbit. 



Development (Fig. 96). The frontal bone is formed in membrane, being deve- 

 loped by two centres, one for each lateral half, which make their appearance, 

 at an early period of foetal life, in the 

 situation of the orbital arches. From 

 this point ossification extends, in a radi- 

 ating manner, upwards into the forehead, 

 and backwards over the orbit. At birth 

 it consists of two pieces, which after- 

 wards become united, along the middle 

 line, by a suture which runs from the 

 vertex to the root of the nose. This su- 

 ture usually becomes obliterated within 

 a few years after birth : but it occasion- 

 ally remains throughout life. 



Articulations. With twelve bones: 

 two parietal, sphenoid, ethmoid; two 

 nasal, two superior maxillary, two lach- 

 rymal, and two malar. 



Attachment of Muscles. The Corrugator Supercilii, Orbicularis Palpebrarum, 

 and Temporal, on each side. 



Fig. 96. Frontal Bone at Birth. 

 Developed by two lateral Halves. 



THE TEMPOEAL BONES. 



The Temporal Bones are situated at the side and base of the skull, and 

 present for examination a squamous, mastoid, and petrous portion. 



The Squamous Portion (squama, a scale), (Fig. 97), the anterior and upper part 

 of the bone, is scale-like in form, and thin and translucent in texture. Its 

 outer surface is smooth, convex, and grooved at its back part for the deep tem- 

 poral arteries ; it affords attachment to the Temporal muscle, and forms part 

 of the temporal fossa. At its back part may be seen a curved ridge part of 

 the temporal ridge; it serves for the attachment of the temporal fascia, limits 

 the origin of the Temporal muscle, and marks the boundary between the 



