1082 



SURGICAL AXD TOPOGRAPHICAL ANATOMY 



In front, the circumference of the bony orbit can be traced in its whole extent. 

 The supraorbital notch lies at the junction of tlie inner and middle thirds of the 

 supraorbital arch, ^\llen this notch is a complete foramen, its detection is much 

 less easy. Above the supraorbital arch is the supraciliary ridge, and higher still 

 the frontal eminence. From the supraorbital notch, a line drawn downwards and 

 slightly outwards, so as to run between the two bicuspid teeth in each jaw, passes 

 over the infraorbital and mental foramina (Holden). The infraorltital foramen 

 lies about a quarter of an inch below the margin of the orbit. The mental foramen 

 in the adult is placed midway between the upper and lower margins of the jaw, 

 and ' is a little over a quarter of an inch below the cul-de-sac of mucous mem- 

 brane between the lower lip and the jaw " (Treves). 



THE BONY SINUSES. — The frontal. — The development of these by the j:wen- 

 tieth or twenty-fifth year may render a fracture here much less grave in the adult 

 than Avould otherwise be the case, the inner table, if now separated from the outer, 

 protecting the brain. Mr. Hilton showed that the absence of any external prom- 

 inence here does not necessarily imph' the absence of a sinus, as this may be formed 



Fig. 660. — Temporal Bone, showing Suprameatal Triaxgle. (Ban.) 



ROOT OF ZYGOMA 



LATERAL SINUS 



SUPRAMEATAL 

 TRIANGLE 



; 5 POSITION FOR PER- 



-^ FORATING VERTICAL 



LINE OF FA- 

 CIAL NERVE 



by retrocession of the internal table. In old people these sinuses may enlarge by 

 the inner table following the shrinking brain. Again, a very prominent bump here 

 does not necessarily point to the existence of a sinus at all, being due merely to a 

 heaping up of bone. 



When well developed, the frontal sinuses may reach two inches npwards and 

 one and a half inches outwards, occupying the greater part of the vertical jtortion 

 of the frontal bone. When very small, they scarcely extend above the nasal 

 process. Even when present, they are often asymmetrical. The sinuses are 

 separated by a septum. Each sinus narrows downwards into the infundibulum. 

 This ' is deeply placed behind the nasal process of the maxilla and near the inner 

 wall of the orbit. Its termination in the middle meatus is about on a level with the 

 pal))ebral fissure' (Thane and Godlee). 



The communication of tlieso sinuses with the nose accounts for tlie frontal 

 headaches in oz^ena, and the fact that a patient with a C(jmpound fracture oi)ening 

 up the sinuses can blow out a flame held close by. 



The mastoid sinuses are arranged in tAvo groups, of the utmost importance in 



