454 THE BRAIN 



removal of the brain its connection with that body was 

 severed. 



Substantiae Perforate Anteriores. These are small 

 triangular districts of grey matter, one on each side. Each 

 is bounded posteriorly by the uncinate extremity of the hippo- 

 campal gyrus ; anteriorly by the diverging striae of the 

 olfactory tract ; and medially by the optic tract. Laterally 

 it passes into the roof of the lateral fissure, and is perforated 

 by the antero-lateral basal arteries. The grey matter in this 

 area is continuous above with the grey matter of the lentiform 

 nucleus (O.T. lenticular). 



Lamina Terminalis. If the anterior border of the optic 

 chiasma is displaced posteriorly a thin lamina will be noticed. 

 It passes upwards from the chiasma into the longitudinal 

 fissure, to become connected with the rostrum of the corpus 

 callosum. This is the lamina terminalis. It closes the third 

 ventricle anteriorly, and is continuous on either side with the 

 grey matter of the substantia perforata anterior. 



Superficial Origins of the Cerebral Nerves. Twelve 

 cerebral nerves are enumerated arising from the brain on either 

 side of the median plane. They are the olfactory or first ; 

 the optic or second ; the oculo-motor or third ; the troch- 

 lear or fourth ; the trigeminal or fifth ; the abducent or 

 sixth ; the facial or seventh ; the acustic or eighth ; the 

 glosso-pharyngeal or ninth; the vagus or tenth ; the accessory 

 or eleventh ; and the hypoglossal or twelfth. 



Each of these nerves is said to have a " superficial " and a 

 " deep " origin. By the term " superficial origin " is meant 

 the region where its fibres enter or leave the brain surface ; 

 the term " deep origin " indicates the connections which are 

 established by the fibres of the different nerves with nuclei or 

 clusters of nerve-cells within the substance of the brain. These 

 nuclei are of two kinds: (i) those in connection with which 

 the afferent or entering nerve fibres end; and (2) those from 

 which the efferent or emerging nerve fibres arise. It is the 

 superficial attachments only which come under notice of the 

 dissector at the present time. 



No fewer than eight of the cerebral nerves have a superficial 

 attachment to the ventral part of the hind brain which is 

 formed by the medulla oblongata and the pons. 



Hypoglossal Nerve. Upon the lateral aspect of the 

 medulla oblongata, in its upper half, is a very conspicuous 



