62 OS FRONTIS. 



tended, on which the eyebrows are placed. Very little above 

 the internal end of each of these superciliary ridges, a protuber- 

 ance may be remarked in most skulls, called the superciliary or 

 nasal boss, where there are large cavities within the bone, called 

 sinuses. Between the internal angular processes, and in front 

 of the vacuity for the ethmoid bone, the edge of the os frontis 

 is serrated for articulation with the ossa nasi, and the process 

 of the upper maxillary bone ; ad from the centre of this sur- 

 face a small process arises, which is called the nasal spine. 

 From the under part of the superciliary ridges, the frontal bone 

 runs a great way backwards : these parts are called orbitar 

 processes, which, contrary to the rest of this bone, are concave 

 externally, for receiving the globes of the eyes, with their 

 muscles, fat, &c. 



In each of the orbitar processes, at the upper and outer 

 portion of the orbit, a considerable sinuosity is observed, where 

 the glandula lachrymalis is lodged. Near each internal angular 

 process a small pit may be remarked, where the cartilaginous 

 pulley of the superior oblique muscle of the eye is fixed. 

 Between the two orbitar processes, there is a large vacuity 

 which the cribriform part of the os ethmoides occupies. The 

 frontal bone has frequently little caverns formed in it where it is 

 joined to the ethmoid bone. 



The foramina, or holes, observable on the external surface of 

 the frontal bone, are'three in each side. 



On each supra-orbital ridge, 3 fig. 10, at the distance of one- 

 third of its length from the nose, is a foramen, or a notch, 

 through which pass a branch of the ophthalmic artery and a 

 small nerve called the supra-orbital. 



In the internal edge of each orbitar process are two other 

 foramina denominated anterior and posterior orbitar, or eth- 

 moidal foramina, which lead to the nose : sometimes they are 

 only notches or grooves which join with similar grooves in the 

 bones below, and form foramina. They transmit the anterior 

 and posterior ethmoidal arteries and veins, and the former trans- 

 mits likewise the internal nasal branch of the ophthalmic nerve. 



The internal surface of the os frontis is concave, except at 



