THE CRANIUM. 125 



ing protected by the external angular process: this depression 

 contains the lachrymal gland. Half an inch above the lower 

 margin of the internal angular process, a much smaller depres- 

 sion exists, occasioned by the tendon of the superior oblique 

 muscle where it plays upon its trochlea. In the orbitary ridge, 

 just without the latter depression, is the supra-orbitary foramen 

 or notch, for the passage of the frontal artery and nerve. 



The internal margins of the orbitar processes are broad and 

 cellular, where they join the ethmoid bone; and at their fore 

 part is seen a large opening on each side leading into the 

 frontal sinus. These margins, in common with the ethmoid 

 bone, form two foramina, one anterior, another posterior, and 

 called internal orbitary; the first transmits the internal nasal 

 branch of the ophthalmic nerve and the anterior ethmoidal 

 artery and vein, the latter transmits the posterior ethmoidal 

 artery and vein. Externally and behind, the orbitar process 

 presents a broad triangular serrated surface for articulating 

 with the sphenoid bone. 



The interior or cerebral face of the os frontis is strongly 

 marked by depressions corresponding with the convolutions of 

 the brain; on its middle exists a vertical ridge, becoming more 

 elevated as it approaches the ethmoidal bone. This ridge is 

 situated below, extends about one-half of the length of the 

 bone, and terminates, above, in a superficial fossa, made by 

 the longitudinal sinus of the dura mater; at its lower extremity 

 is the foramen caecum, common to it and the ethmoid bone, 

 and which is occupied by a process from the great falx of the 

 dura mater, and also affords passage to some very small veins, 

 which go from the nostrils to the commencement of the longi- 

 tudinal sinus.* 



The frontal sinuses consist in one or more large cells, placed 

 beneath the nasal protuberances. There is a very great 

 variety in their magnitude and extent; sometimes they proceed 

 as far outwards as the external angular process, and back- 

 wards for half an inch into the orbitar plates. In a few 

 instances in the adult they do not exist, but the cases are very 

 uncommon. The cells of the opposite sides have a complete 



* Portal. Anat. Medicalo. 

 11* 



