THE FRONTAL BONE 



77 



in the same subject. The whole surface of the bone above this part is smooth, 

 and covered by the aponeurosis of the Occipitofrontalis muscle. Below the frontal 

 eminence and separated from it by a slight groove is the superciliary ridge (arcus 

 superciliaris), 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 air sinuses, 1 and give attachment to the Orbicularis 

 palpebrarum and Corrugator supercilii. Between the two superciliary ridges 

 is a smooth, flat surface, the glabella. Beneath the superciliary ridge is the 

 supraorbital arch (margo supraorbitalis), a curved and prominent margin, which 

 forms the upper boundary of the orbit and separates the vertical from the hori- 

 zontal 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; 



I 



-. , External 



angular process. anguiar proce ss. 



Nasal spine. 

 FIG. 44. Frontal bone. Outer surface. 



the inner part is less prominent. At the junction of the internal and middle 

 third of this arch is a notch, sometimes converted into a foramen, and called the 

 supraorbital notch (incisura supraorbitalis). 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. To the median 

 side of the supraorbital notch there is often a notch (incisura frontalis) for the 

 passage of the frontal artery and nerve. The supraorbital arch terminates 

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



1 Some confusion is occasioned to students commencing the study of anatomy 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. 



