The mortality varies also according to the _fossa_ implicated. Thus, to each fossa there are certain peculiar dangers--to the _anterior_ fossa, meningeal infection from the nose, frontal and ethmoidal sinuses; to the _middle_ fossa, meningeal infection from the naso-pharynx and ear, and hæmorrhage from the middle meningeal and internal carotid arteries, and from the cavernous venous sinus; and to the _posterior_ fossa, laceration of the lateral and sigmoid venous sinuses. After such consideration of local complications, it would appear that the middle fossa of the skull presents the greatest dangers. Another factor must, however, be taken into consideration--injury to the brain--the commonest cause of death in all head injuries. The main vital centres are grouped in the region of the fourth ventricle, and Leonard Hill has proved that any increase in the intracranial pressure exerts its influence most rapidly and most effectually when the lesion is situated beneath the tentorium cerebelli. One may assume, therefore, that fractures of the posterior fossa are the most dangerous, and that those involving the anterior fossa hold out the best prognosis. In the case of pure or primary vault fractures the mortality may be estimated by reference to the following table. It is composed from 88 cases admitted into St. Bartholomew’s Hospital between the years 1900 and 1906. Under the age of 5 8 lived and 2 died. Mortality, 20 per cent. „ „ 10 2 „ „ 3 „ „ 60 „ „ „ 15 6 „ „ 0 „ „ 0 „ „ „ 20 10 „ „ 3 „ „ 23 „ „ „ 30 9 „ „ 1 „ „ 10 „ „ „ 40 16 „ „ 9 „ „ 36 „ „ „ 50 3 „ „ 7 „ „ 70 „ „ „ 60 2 „ „ 1 „ „ 33 „ Over the age of 60 3 „ „ 3 „ „ 50 „ 59 lived and 29 died. Mortality, 37 per cent. ============================================= For the remote effects of skull fractures, see Chapter VI. [17] _Brit. Med. Journ._, September 11, 1909, p. 645. [18] Chassaignac, _Plans de la Tête_, 1842. [19] _Milligan, Trans. of the Otolog. Soc._, vol. viii, p. 69. [20] _Boston City Hosp. Reports_, 1894. [21] Delfau and Günther narrate a case in which death occurred from pressure on the tenth nerve. (_Deutsche Klinik_, Berlin, 1853.) [22] _System of Surgery_, vol. i, p. 93. [23] _Surgical Experiences in South Africa._ [24] _Edin. Med. Journ._, 1909, p. 526. [25] _Johns Hopkins Hospital Bulletin_, April, 1909. CHAPTER V INTRACRANIAL INJURIES: EXTRA- AND SUB-DURAL HÆMORRHAGES. INJURY TO THE BRAIN HÆMORRHAGES I. Extra-dural hæmorrhage.