THE CRANIUM. 23 



tion of the temporal bone (6). The floor of the sella turcica and the lateral walls of the body of 

 the sphenoid bone should also be mentioned here, as they are thin walls of the large sphenoidal 

 sinuses (/) (see page 52). In the posterior cranial fossa the bone is thinnest at the bottom of the 

 fossa (e). The osseous layer separating the lateral sinus from the mastoid cells is often very 

 thin, and this is a fact of great practical importance (see page 59). 



Particularly strong portions o\ the base are to be found : In the median line : the crista galli, 

 the clivus [i. e., the body of the sphenoid between the dorsum sellae and the basilar portion of the 

 occipital. ED.], the internal and external occipital protuberances, and the internal and external 

 occipital crests. Laterally : the great wing of the sphenoid, with the exception of its base, and 

 the anterior and middle parts of the petrous portion of the temporal bone with the cochlea and 

 labyrinth. 



From the preceding statements it will be observed that the middle cerebral fossa is relatively 

 the weakest and therefore predisposed to fractures which often involve the nerves passing along 

 the base of the brain in this situation (see page 32 and Fig. 9). If the thinness of the orbital roof 

 is appreciated (see Fig. 16), it will be readily understood how easy it is for a punctured wound to 

 pass the eyeball, perforate the roof of the orbit, and penetrate into the frontal lobe of the brain. 



Although injuries of the brain are generally accompanied by injuries of the surrounding 

 bones, a study of the base of the cranium shows that it is possible for a fine-pointed instrument 

 to enter the orbit, pass through the sphenoidal fissure or the optic foramen, and injure the brain 

 without producing a fracture of the bone. 



It will also be understood that fractures of the cribriform plate of the ethmoid (i. e., the nasal 

 roof) may lead to hemorrhage from the nose, and that cerebrospinal fluid may escape through 

 the nose if the membranes of the brain are lacerated. The same thing may occur in fractures of 

 the middle fossa, where, after laceration of the wall of the sphenoidal sinus which opens into the 

 superior meatus of the nose (see page 53, Fig. n, Fig. 19, and Plate 4), there is not only an escape 

 of cerebrospinal fluid, but where even a rapid and fatal nasal hemorrhage has been observed 

 from a rupture of the internal carotid artery which lies in close relation with the wall of the sinus 

 (see pages 31 and 34). If the line of fracture strikes the optic foramen, the ophthalmic artery 

 may give rise to a large effusion of blood into the orbit [producing a subconjunctival ecchymosis, 

 more rarely exophthalmos. ED.]. The escape of blood or cerebrospinal fluid from the ear 

 presupposes a fracture of the tegmen tympani and a laceration of the drum-membrane [the bloo'd 

 coming from the vessels of the tympanum or from one of the neighboring sinuses. ED.], or the 

 blood may come from the sigmoid sinus, reaching the middle ear by way of the air-cells in the 

 mastoid process (see page 31 and Fig. 22). In this case blood from the posterior cranial fossa 

 may escape from the nose or mouth, consequently a fracture of any of the three cranial fossas may 

 cause a hemorrhage from the nose, for it must be remembered that with an intact drum-membrane, 

 the blood poured out into the middle ear may reach the nasal or oral cavity through the Eustachian 

 tube and escape from the nose or mouth (see Plate 4 and Fig. 19). 



[Cerebrospinal fluid escapes from the ear when, in addition to the fracture of the petrous bone 

 and tear of the tympanic membrane, there has occurred a rent in the dura and arachnoid or their 

 prolongations into the internal auditory meatus through which the subarachnoid space com- 

 municates with the tympanum. A serous discharge derived from the mastoid cells or consisting 



