THE SKULL. 



they are well developed. They may extend well out over the orbits, reaching to 

 within a short distance of the temporal ridge, while in other instances they do not go 

 beyond the supra-orbital notches. In height they may reach the lower portion of 

 the frontal eminences or may cease at the level of the superciliary ridges. The size 

 of the sinus cannot be judged from the size of the bony prominences. Neither is the 



Mastoid antrum 



Suprameatal spine 



Mas 

 FIG. 16. Surface chipped away to show the tnastoid antrum and cells, the latter unusually well developed. 



size nor sex of the individual any criterion. In a small female we have seen them of 

 considerable size. When diseased sufficiently to give rise to symptoms, they will be 

 found to be quite large. They are separated from each other by a septum, and if 

 extensive are divided into several pockets or recesses. They open into the infundib- 



Superior longitudinal sinus 



Inferior longitudinal sinus 



Straignt sinus 

 Torcular Herophili 



Lateral sinus 

 'Occipital sinus 



v Superior petrosal sinus 

 'Sigmoid sinus 

 Inferior petrosal sinus 

 Jugular vein Cavernous sinus 

 FIG. 17. The cerebral blood sinuses. 



ulum, at the anterior extremity of the middle turbinated bone in the middle meatus 

 of the nose. Fracture of the outer wall of the sinus not infrequently occurs without 

 involving the inner table. 



Mastoid Process. The mastoid process is continous with the superior curved 

 line of the occiput. It increases in size from the time of birth, but is composed of 

 cancellous tissue until after the age of puberty, when the mastoid cells develop. The 

 mastoid antrum, a cavity five millimetres in size at birth, which opens into the upper 

 posterior portion of the tympanum, is relatively larger at birth than in the adult. 



