THE BASE OF THE BRAIN 391 



ated areas are small triangular districts of grey matter, one 

 on each side. Each is bounded, posteriorly, by the uncinate 

 extremity of the hippocampal 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 central 

 arteries (Figs. 147, 149). The grey matter of each anterior 

 perforated area is continuous, above, with a mass of grey 

 matter in the base of the corresponding cerebral hemisphere 

 which is called the corpus striatum (Fig. 185). 



Lamina Terminalis. The lamina terminalis, which was 

 originally the anterior wall of the brain, will be displayed if 

 the optic chiasma is pulled gently backwards. It is a thin 

 lamina which passes upwards from the chiasma into the longi- 

 tudinal fissure, to become connected with the rostrum of the 

 corpus callosum. It closes the third ventricle anteriorly, and 

 is continuous, on each side, with the grey matter of the sub- 

 stantia perforata anterior (Fig. 186). 



Superficial Attachments of the Cerebral Nerves. Twelve 

 cerebral nerves arise from or enter the brain, on each side of 

 the median plane. They are the olfactory or first, consisting 

 of about twenty separate filaments ; the optic or second ; the 

 oculo-motor or third ; the trochlear or fourth ; the trigeminal or 

 fifth; the abducent or sixth; the facial or seventh ; the acoustic 

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

 the accessory or eleventh ; and the hypoglossal or twelfth. 



A thirteenth pair of cerebral nerves, called the nervi terminates ; is 

 known. Each nervus terminalis is attached to the cerebrum posterior 

 to the olfactory stride. Its fibres run alongside the corresponding olfactory 

 tract, and are distributed with the olfactory nerves to the upper parts of 

 the wall of the nasal cavity-. The functions of the nervi terminales are 

 unknown. 



Each nerve is said to have a " superficial attachment " and 

 a "deep" origin or termination. By the term "superficial 

 attachment " is meant the region where its fibres enter or leave 

 the brain surface ; the terms " deep termination and origin " 

 indicate 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. The 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 

 in 25 b 



