OS FRONTIS. 63 



the orbitar processes, which Fig. 11.* 



are convex, and support the 

 anterior lobes of the brain. 

 This surface is not so smooth 

 as the external ; for the larger 

 branches of the arteries of 

 the dura mater make some 

 furrows in its sides and back 

 parts, and its lower and fore 

 parts are marked with the 

 convolutions of the anterior 

 lobes of the brain. In the 

 middle of the concave inter- 

 nal surface is a groove, which 

 is small at its commencement, and gradually increases in dia- 

 meter as it proceeds upwards. This is formed by the superior 

 longitudinal sinus ; at its commencement is a ridge to which the 

 beginning of the falciform process of the dura, mater is attached. 

 At the root of this ridge is a small foramen, sometimes formed 

 jointly by this bone and the ethmoid ; it is denominated fora- 

 men ccECum ; in it a small process of the falx is inserted, and 

 here the longitudinal sinus begins. 



The frontal sinuses are formed by the separation of the two 

 tables of this bone at the part above the nose and the internal 

 extremities of the superciliary ridges. In the formation of these 

 cavities, the external table commonly recedes most from the 

 general direction of the bone. 



* The internal surface of the frontal bone ; the bone is raised in such a man- 

 ner as to show the orbito-nasal portion, i. The grooved ridge for the lodgment 

 of the superior longitudinal sinus and attachment of the falx. 2. The foramen 

 caecum. 3. The superior or coronal border of the bone ; the figure is situated 

 near that part which is bevelled at the expense of the internal table. 4. The 

 inferior border of the bone. 5. The orbital plate of the left side. 6. The cellu- 

 lar border of the ethmoidal fissure. The foramen ceecum (2) is seen through 

 the ethmoidal fissure. 7. The anterior and posterior ethmoidal foramina ; the 

 anterior is seen leading into its canal. 8. The nasal spine. 9. The depression 

 within the external angular process (12) for the lachrymal gland. 10. The de- 

 pression for the pulley of the superior oblique muscle of the eye ; immediately 

 to the left of this number is the supra-orbital notch, and to its right the internal 

 angular process. 11. The opening leading into the frontal sinuses. 12. The 

 same parts are seen upon the opposite side of the figure. 



