Besides the extreme form of Encephalocele (see p. 49) certain cases of Hernia cerebri, in which there is no hydrocephalus, are regarded as belonging to this class. Sometimes also masses of grey substance are met with in abnormal situations, as in the midst of the corona radiata. Some of these cases-may really be tumours of the brain, but they are congenital, and due to errors in development.

Forencephalus is a term used for defects of the brain in the form of gaps in the superficial parts penetrating more or less deeply into the cerebral substance, sometimes as deeply as the ventricles. The gaps are occupied by the cedematoua membranes. The lesion is ascribed to inflammation occurring in the foetus. There may be associated with it a congenital paralysis and atrophy of parts corresponding with the lesion in the brain.

In cases of Idiocy there is defect of the brain, and it may be in various forms. There may be micrencephalus or congenital hydrocephalus, or partial defects. There may be little beyond some traces of inflammation in the membranes. Similarly Cretinism, which is endemic in some localities an€ is often associated with goitre, is related to various lesions of the brain. In this condition, however, the defect in the brain seems to depend on the condition of the bones. The skeleton as a whole is stunted and deformed, and the bones of the skull show synostosis and premature synchondrosis, so that the elongation of the basal parts and expansion of the vault are variously hindered, the brain being correspondingly defective.

Literature

For greater defects see under Malformations. Micrencephalus - Virchow, Gesam. Abhand., 1856, p. 891; Hitzig in Ziemssen's Encyclopaedia (with literature); Aeby, Mikrocephalie und Atavismus, 1878; Bourneville, Bull, de la Soc. anat. de Paris, x., 1896. Defect of cerebellum - Fraser, Glas. Med. Jour.r xiii., 1880; Gould, Path. Trans., xxxiii., 6; Clapton, Path. Trans., xxxii., 20. Hypertrophy - Hitzio, loc. cit.; Virchow, Ges. Abhandl., 1856, Virch. Arch., xxxiii.; Lees, Dubl. Med. Jour., xxii., 1842; Tuke, Jour, of Anat. and Phys., xii., 1873; Landouzy, Gaz. fhed. de Paris, No. xxvi., 1874. Heterotopia - Hitzig, 1. c.; Virchow, 1. c, and Virch. Arch., xxxviii., 1886; Meschede, Virch. Arch., lvi., 1872; Simon, Virch. Arch., lviii., 1883. Porence-phalus- Heschl, Prag. Vierteljahrschr., 1868, and Jahrb. f. Kinderheilk., xv., 1880; De la Croix, Virch. Arch., xcvii.; Binswanger, do., cii.