588 ORIGIN OF THE ENCEPHALIC NERVES. 



together the convolutions placed above that part ; and the 

 intercerebral commissure or valve of Vieussens, which has already 

 been described. A laterel view of the different parts of the 

 brain, is seen in the vertical section opposite, as well as the 

 position of the ventricles, the channel of communication between 

 them, and the relative position of the encephalic nerves at 

 their origin. 



Where the brain is reversed, we observe at its base a deep 

 fissure, which separates the anterior from the middle lobes. This 

 is called the Fissure of Sylvius, and lodges the lesser wings of 

 the sphenoid bone, and the middle cerebral artery. By tracing 

 this fissure outwards, we fall upon an isolated cluster of five or 

 six convolutions, called the Island of Reil, which forms the 

 bottom structure to the corpus striatum. 



At the inner end of the fissure of Sylvius, is a triangular plane 

 of medullary matter, pierced by blood-vessels, which run into 

 the corpus striatum ; it is called the substantia perforata. 

 Immediately behind the optic commissure, and in front of the 

 eminentia mammillares, is found a small mass of grey matter, 

 called the tuber cinereum, which forms part of the floor to the 

 third ventricle. 



The infundibulum is a funnel-shaped reddish cineritious cord, 

 two and a half lines long, which seems to spring from the tuber 

 cinereum at the base of the third ventricle, and terminates on the 

 pituitary gland. It presents an open cavity on the side of the 

 third ventricle, and in the foetus communicates with the cavity 

 in the gland ; after birth its inferior extremity appears to be 



ventricles, and the septum lucidum have been removed.) Between the tuber- 

 cula quadrigemina and the pons is the aqueduct of Sylvius, or the passage from 

 the third ventricle to the fourth, which forms the cavity, m. between the cere- 

 bellum and the medulla oblongata. 1, Olfactory nerve. 2, The eye, upon 

 which terminates the optic nerve, the root of which may be traced back, over 

 the eras cerebri to the optic thalamus, and the nates. Next below the optic is 

 seen the third pair of nerves, motor oculi. 4, The fourth pair running to the 

 superior oblique muscle of the eye. 5, Superior maxillary branch of the fifth 

 pair. 5', Ophthalmic branch of the fifth pair. 5", Inferior maxillary branch of 

 the fifth pair. 6, Sixth pair, or motor externus. 7, Facial or portio dura ; 

 below the origin of this is seen the trunk of the auditory nerve, or portio mollis. 

 9, Glosso-pharyngeal. 10, Pneumogastric. 11, Hypo-glossal. 12, Spinal 

 accessory of Willis. 14, 15, Cervical nerves. The ophthalmic ganglion is 

 seen near the eye at the outer side of the optic nerve. 



