540 



THE NEBVOUS SYSTEM. 



is closely applied to the internal aspect of the cranial vault, and are separated from 

 each other by a deep median cleft, termed the fissura longitudinalis cerebri, which 

 extends from the front to the back of the brain. 



The inferior aspect of the brain is usually termed the basis cerebri. It presents 

 an uneven and irregular surface, which is more or less accurately adapted to the 

 inequalities on the floor of the cranial cavity. Upon this aspect of the brain some 

 of its main subdivisions may be recognised. Thus, posteriorly, is seen the short 

 cylindrical portion, called the medulla oblongata, through which, at the foramen 

 magnum, the brain becomes continuous with the medulla spinalis. The medulla 

 oblongata lies on the ventral aspect of the cerebellum, and occupies the vallecule 

 or hollow which intervenes between the two cerebellar hemispheres. The cerebellun 



Optic chiasma 



Infundibulur 



Olfactory bulb 



Left corpus mamillare 



Substantia perforata 

 posterior 



Pedunculus cerebri 



Abducens nerve 



Hypoglossal nerve 



Olfactory tract 



Optic nerve, 



Substantia perforata 

 anterior 



Optic tract 



Tuber cinereum 

 Oculomotor nerve 



Trochlear nerve 

 Trigeminal nerve 



Facial nerve 

 Acoustic nerve 

 ' Nervus intermedius 

 Glosso-pharyngeal nerve 



Vagus nerve 



MEDULLA OBLONGATA "^^BB^^^" "^^^^^^^^^ Accessory nerve 



Medulla spinalis (cut) Hypoglossal nerve 



FIG. 476. THE BASE OF THE BRAIN WITH THE CEREBRAL NERVES ATTACHED. 



is a mass of considerable size which is placed below the posterior portions of tt 

 two cerebral hemispheres. It is easily recognised on account of the closely se 

 curved, and parallel fissures which traverse its surface and give it a foliate 

 appearance. Above the medulla oblongata, and in close connexion with it, is 

 prominent white elevation called the pons. Immediately in front of the pons thei 

 is a deep hollow or recess. This is bounded behind by the pons, on each side b 

 the projecting temporal lobe of the cerebral hemisphere, and in front by the orbit* 

 portions of the frontal lobes of the cerebral hemispheres. Passing out from eac 

 side of the anterior part of this recess is the deep lateral fissure of the brain whic 

 intervenes between the pointed and projecting extremity of the temporal lot 

 and the frontal lobe of the cerebrum, whilst, in the median plane in front, tt 

 longitudinal fissure, which separates the frontal portions of the cerebral hemisphere 

 opens into it. 



Within the limits of this deep hollow, on the base of the brain, two large rop< 



