1208 I HUMAN ANATOMY. 



Tlie oac h v common enlargement of the head, hydroeephalus, is due to a retention 

 of cerebr ilir ly r0 ' fluid within the cranium, ordinarily within the ventricles, but some- 

 times VD w ith tHbarachnoid space. It is usually a congenital condition ; its cause 

 is not fjj n theJF lown - ^ ls believed by many that it is due to a prenatal inflam- 

 mation ver tj ventricular ependyma, and by others to a disarrangement of the orifices 

 of communication between the ventricles (Luschka, Monro, and Neurath). The 

 aqueduct of Sylvius has been found obliterated, and inflammatory processes have 

 been seen about the foramen of Monro. 



Congenital defective ossification of the skull may result in a gap through which 

 may protrude a portion of the meninges with or without brain substance. If such a 

 protrusion consists of a meningeal sac containing only fluid, it is called a meningocele. 

 If it contains a portion of the brain also, it is an encephalocele, and if the protruded 

 portion of the brain encloses a portion of a ventricle, a hydrenccphahcele. Such 

 tumors may be concealed from view at the base of the skull, or in the pharynx, or 

 may protrude into the nose or orbit. They are usually in the median line and most 

 frequently in the occipital region. Next in frequency they occur at the fronto-nasal 

 suture, and more rarely in other parts of the skull. Pressure on the tumor will often 

 reduce it partly or completely within the cranium, but in the latter case symptoms of 

 pressure on the brain will arise. Violent expiratory efforts, as in crying or coughing, 

 which increase the cerebral congestion, render the tumor more tense. 



The Meninges. Diseases of the meninges are relatively more common than 

 those of the brain proper, and many conditions often spoken of as brain diseases are 

 affections of the meninges, the pia being closely adherent to the brain and extending 

 into the fissures. Inflammation of the dura is called pachy meningitis, of the pia and 

 arachnoid together lepto-meningitis. 



External pachymeningitis is usually secondary to disease of the cranial bones, 

 traumatism, infection, or tumors. It is most frequently the result of ear disease, and 

 is therefore generally of surgical interest. 



Internal pachymeningilis is apt to be associated with effusions of blood into the 

 subdural space ; they may cover a considerable area without producing marked symp- 

 toms, or they may be encapsulated (haematomata of the dura mater), and may reach 

 the size of a man's fist, causing compression of the brain. Occasionally they become 

 purulent. The blood or pus may gravitate to the base of the brain in the region of 

 the cerebellum, pons, and medulla, when the pressure symptoms will be more serious ; 

 or it may find its way into the spinal canal. 



The dura is especially adherent at the base of the skull and, to some degree, at 

 the sutures of the vault. In the rest of the vault it is loosely attached, and accord- 

 ing to Tillaux, particularly so in the temporal region. Collections of blood may 

 accumulate between the dura and the bone {extradural hemorrhage}. This variety 

 of intracranial hemorrhage is commonly the result of rupture of one of the branches 

 of the middle meningeal artery in the temporal region, the effused blood separating 

 the loosely attached dura. If the blood is poured out rapidly, compression 

 symptoms will soon appear, but if the hemorrhage is slow, the escape of cerebro-spinal 

 fluid into the spinal canal permits of more delay in the appearance of those symptoms. 

 The patient has often time to recover, at least partially, from the unconsciousm >s 

 of concussion before that of compression appears ; and it is this recovery of intelligence 

 which is most characteristic of the condition. There will often be locali/ing symptoms 

 indicating the part of the brain cortex which is irritated or compressed. 



Sithdural hi'morrhagc may follow the rupture of a number of small vessels, either 

 of the pia or dura under a depressed fracture ; or it may come from a large vessel, 

 particularly the middle cerebral. The symptoms and treatment are very much the 

 same as in the extradural variety. 



In children extradural hemorrhage is very rare, because of the relatively tinner 

 attachment of the dura during the period of growth. The blood may escape under 

 tin- scalp through a Hue of fracture in the skull ; or, what is more likely, it may pass 

 through a tear iu the dura into the subdural space. In fractures of the base of the 

 skull, at any age, owing to the adhesion of the dura, the latter is likely to be torn ; 

 rerebro-spinal fluid may escape into the adjacent air cavities, as into the nose, pharvnx 

 or middle ear. A close adhesion of the dura to the bone, as sometimes found at 



