240 HUMAN ANATOMY. 



cranium proper, while behind it are the thickening of the basilar process and the 

 posterior clinoid plate (Humphry) (Fig. 254). 



The differential symptoms of fracture through the floors of these fossa; are 

 determined by their anatomical relations. They are as follows : 



I. Anterior Cerebral Fossa. — i^a) Epistaxis when the Schneiderian membrane, 

 and the dura and arachnoid are torn. It should not be forgotten that the blood may 

 come from the mucous membrane alone. ( b) Loss of smell from injury to the 

 olfactory bulbs resting on the cribriform plate, {c) Subconjunctival ecchymosis. 



The blood is usually derived from the meningeal vessels over the orbital plates, 

 but in bad cases may come from the ophthalmic artery, ophthalmic vein, or cavern- 

 ous sinus. If the body of the sphenoid is fractured, the blood may find its way 

 through the sphenoidal sinuses into the pharynx and stomach, and then be vomited, 

 giving rise to a mistaken diagnosis of gastric injury. 



t 2. Middle Cerebral Fossa. — {a) Hemorrhage from the ear. This may be 

 merely from a torn tympanic membrane, (b) Escape of cerebro-spinal fluid from 

 the ear. This indicates that the petrous portion of the temporal is broken, the dura 

 mater and the arachnoid torn, and the membrana tympani ruptured. If the latter 

 escapes injury, the fluid may trickle into the throat through the Eustachian tube, 

 (c) In rare and very severe cases the lateral sinus has been opened or the internal 

 carotid torn, {d) There may be deafness or facial paralysis, or both. 



3. Posterior or Cerebellar Fossa. — {a) Hemorrhage into the pharynx if the 

 basilar process is involved and the pharyngeal mucous membrane torn, {^b) Ecchy- 

 mosis at the nape of the neck and about the mastoid. 



Of course the characteristic symptoms of any two or even of all three of these 

 injuries may be commingled if the fracture is extensive enough. 



Just as fractures would be more frequent were it not for the mechanism that has 

 been described, so concussion or laceration of the brain would occur far oftener 

 were it not for certain factors, among which are the different strata of varying 

 density intervening between the brain and the outer surface of the scalp. The soft 

 diploe and the dense inner "vitreous" table both tend to diminish shock to the 

 brain, the former by arresting vibrations and the latter by lateralizing them. The 

 eminences on the inner surface of the skull project into the spaces between the great 

 divisions of the brain, where, in places, there is more subarachnoid fluid than else- 

 where ; such elevations are intimately connected at their edges and terminal points 

 with the strong expansions of the dura mater, — the fal.x and the tentorium, — which 

 still further take up and distribute the final vibrations. ' ' Thus there is every facility 

 for causing jarring impulses to deviate from the direct line and take a circumferential 

 route, in which they are gradually weakened and rendered harmless" (Humphry). 



The conditions tending to minimize the effects of violence inflicted upon the 

 skull are thus summarized by Jacobson : "(i) The" density and mobility of the 

 scalp. (2) The dome-like shape of the skull. This, like an egg-shell, is calculated 

 to bear hard blows and also to allow them to glide off. (3) Before middle life the 

 number of bones tends to break up the force of a blow. (4) The sutures interrupt 

 the transmission of violence. (5) The internal membrane (remains of foetal peri- 

 osteum) acts in early life as a linear buffer. (6) The elasticity of the outer table. 

 (7) The overlapping of some bones, — e.g., the parietal by the squamous ; and the 

 alternate bevelling of adjacent bones, — e.g., at the coronal suture. (8) The pres- 

 ence of ribs or groins, — e.g., (a) from the crista galli to the internal occipital pro- 

 tuberance ; {b) from the root of the nose to the zygoma ; (c) the temporal ridge 

 from orbit to mastoid ; (d) from mastoid to mastoid ; (e) from the external occipital 

 protuberance to the foramen magnum. (9) Buttresses, — e.g., malar and zygomatic 

 processes, and the greater wing of the sphenoid. (10) The mobility of the head 

 upon the spine." 



Landmarks. — The prominence of the occiput, of the parietal region, or of the 

 frontal eminence indicates in a general way the development of the corresponding 

 po'"tions of the brain. 



The terms used to designate particular points on the skull have already been 

 described (page 228); additional attention may here be paid to those of especial 

 importance as landmarks. 



