28 FRONTAL BONE. 



which correspond with the convolutions of the anterior lobes of the 

 cerebrum. The superior border is thick and strongly serrated, bevel- 

 led at the expense of the internal table in the middle, where it rests 



Fig. 16.* 



upon the junction of the two parietal, and at the expense of the exter- 

 nal table, on each side, where it receives the lateral pressure of those 

 bones. The inferior border is thin, irregular, and squamous, and 

 articulates with the sphenoid bone. 



Development. By two centres, one for each lateral half. Ossifica- 

 tion begins in the orbital arches, somewhat before the vertebrae. The 

 two pieces are separate at birth, and unite by suture during the first 

 year, the suture sometimes remaining permanent through life. The 

 frontal sinuses make their appearance during the first year, and increase 

 in size until old age. 



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

 ner as to show the orbito-nasal portion. 1. The grooved ridge for the lodg- 

 ment 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 cellular border of the ethmoidal fissure. The foramen caecum (2) is seen 

 through the ethmoidal fissure. 7. The anterior and posterior ethmoidal fora- 

 mina; 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 depression 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. 1 1 . The opening leading into the frontal 

 sinuses. 12. The same parts are seen upon the opposite side of the figure. 



