34 



BONES OF THE HEAD. 



varying prominence immediately above the margin of the orbit. Between 

 the superciliary ridges is the nasal eminence or gldbella. The margin of the 

 orbit, the orbital arch, is most defined towards its outer part j it presents 

 towards its inner third the supra-orbital notch, sometimes converted into a 

 foramen, which transmits the supra-orbital nerve and artery. The ex- 

 tremities of the orbital arch point downwards, and form the internal and 

 external angular processes. The internal angular process is slender ; the 

 external is thick and strong, and articulates with the malar bone. The 

 temporal ridge springs from the external aspect of this process, and 

 arches upwards and backwards to be continued on the parietal bone : it 

 separates the temporal from the frontal part of the outer surface of the 

 bone. 



Inferior Surface. The orbital surfaces are somewhat triangular, their 

 internal margins being parallel, while the external are directed backwards 

 and inwards. Close to the external angular process is the fossa lachry- 

 malis, which lodges the lachrymal gland ; and close to the internal angular 

 process is the fovea trochlearis, a small depression to which the pulley of the 

 trochlearis muscle is attached. Between the orbits in front is the serrated 

 surface which articulates with the superior maxillary and nasal bones, and in 

 the middle line a sharp process of variable length, the nasal spine, descends 

 between the latter bones and the central plate of the ethmoid. On the 

 sides of the incisura ethmoidalis, the inner table of the bone extends nearer 

 the middle line than the outer, and the intervening margin is thrown 

 into shallow spaces, which form the roofs of cells in the ethmoid bone. 

 Traversing this margin are two grooves, which complete, with the eth- 

 moid, the anterior and posterior internal orbital foramina. The ante- 

 rior groove transmits the nasal twig of the ophthalmic nerve and the 

 anterior ethmoidal vessels ; the other, the posterior ethmoidal vessels. 

 Further forward, on each side of the nasal spine, is a larger hollow, 



the opening of the frontal 



Fig. 31. sinus, which extends for a 



variable distance behind the 

 superciliary ridges, and which 

 communicates with the cavity 

 of the nose . Outside the orbi- 

 tal surface behind the serrated 

 border for the malar bone, 

 there is a large serrated tri- 

 angular area which articulates 

 with the great wing of the 

 sphenoid. 



Fig. 31. THE FRONTAL BONE 



FROM BEHIND AND BELOW, 

 SHOWING THE INTERNAL CERE- 

 BRAL SURFACE AND THE ROOF 

 OF THE ORBITS. 4 



2, 4, and 5, as in the preceding 

 figure; 9, internal or cerebral 

 surface, slightly marked by cere- 

 bral convolutions and glandular 

 pits; 10, groove of the superior 

 longitudinal sinus, ending below 

 in, 11, the internal frontal crest, which leads down to, 13, the foramen caecum; 12, the 

 orbital plate, the number is placed in the depression for the lachrymal gland; 14, the 



