THE FRONTAL BONE. 171 



Vertical Portion. External Surface (Fig. 135). In the median line, traversing 

 the bone from the upper to the lower part, is occasionally seen a slightly-elevated 

 ridge, and in young subjects a .suture, which represents the line of union of the two 

 lateral halves of which the bone consists at an early period of life; in the adult 

 this suture is usually obliterated and the bone forms one piece ; traces of the 

 obliterated suture are. however, generally perceptible at the lower part. On either 

 side of this ridge, a little below the centre of the bone, is a rounded eminence, the 

 frontal eminence. These eminences vary in size in different individuals, and are 

 occasionally unsymmetrical in the same subject. They are especially prominent 

 in cases of well-marked cerebral development. The whole surface of the bone 

 above this part is smooth, and covered by the aponeurosis of the Occipito-frontalis 

 muscle. Below the frontal eminence, and separated from it by a slight groove, is 

 the superciliary rilge, broad internally, where it is continuous with the nasal 

 eminence, but less distinct as it arches outward. These ridges are caused by the 

 projection outward of the frontal sinuses, 1 and give attachment to the Orbicularis 

 palpebrarum and Corrugator supercilii. Between the two superciliary ridges is a 

 smooth surface, the glabella or nasal eminence. Beneath the superciliary ridge 

 is the supraorbital arch, a curved and prominent margin, which forms the upper 

 boundary of the orbit, and separates the vertical from the horizontal portion of the 

 bone. The outer part of the arch is sharp and prominent, affording to the eye, in 

 that situation, considerable protection from injury; the inner part is less promi- 

 nent. At the junction of the internal and middle third of this arch is a notch, 

 sometimes converted into foramen by a bony process, and called the supraorbital 

 notch or foramen. It transmits the supraorbital artery, vein, and nerve. A small 

 aperture is seen in the upper part of the notch, which transmits a vein from the 

 diploe to join the supraorbital vein. The supraorbital arch terminates externally 

 in the external angular process and internally in the internal angular process. 

 The external angular process is strong, prominent, and articulates with the malar 

 bone ; running upward and backward from it are two well-marked lines, which, 

 commencing together from the external angular process, soon diverge from each 

 other and run in a curved direction across the bone. The lower one. the temporal 

 ridg>-. gives attachment to the Temporal muscle, the upper one to the temporal 

 fascia. Beneath them is a slight concavity that forms the anterior part of the 

 temporal fossa and gives origin to the Temporal muscle. The internal angular 

 processes are less marked than the external, and articulate with the lachrymal 

 bones. Between the internal angular processes is a rough, uneven interval, the 

 nnx'il notch, which articulates in the middle line with the nasal bone, and on either 

 side with the nasal process of the superior maxillary bone. From the concavity 

 of this notch projects a process, the nasal process, which extends beneath the nasal 

 bones and nasal processes of the superior maxillary bones and supports the bridge of 

 the nose. On the under surface of this is a long pointed process, the nasal spine, and 

 on either side a small grooved surface enters into the formation of the roof of the 

 nasal fossa. The nasal spine forms part of the septum of the nose, articulating in 

 front with the nasal bones and behind with the perpendicular plate of the ethmoid. 

 Internal Surface (Fig. 136). Along the middle line is a vertical groove, the 

 edges of which unite below to form a ridge, the frontal crest; the groove lodges 

 the superior longitudinal sinus, whilst its margins afford attachment to the falx 

 cerebri. The crest terminates below at a small notch which is converted into a 

 foramen by articulation with the ethmoid. It is called the foramen ccecum, and 

 varies in size in different subjects : it is sometimes partially or completely 

 impervious, lodges a process of the falx cerebri, and when open transmits a vein 



1 Some confusion is occasioned to students commencing the study of anatomv by the name 

 " sinuses " having been given to two perfectly different kinds of spaces connected with the skull. 

 It may be as well, therefore, to state here, at the outset, that the "sinuses" in the interior of the 

 cranium which produce the grooves on the inner surface of the bones are venous channels along 

 which the blood runs in its passage back from the brain, while the "sinuses" external to the cranial 

 cavity the frontal, sphenoidal, ethmoidal, and maxillary ) are hollow spaces in the bones themselves 

 which communicate with the nostrils, and contain air. 



