416 A. Sanders. Anatomy of Central Nervous System. [May 23, 

 Ventricles : — 



The fourth ventricle consists of two parts, one part beneath the cere- 

 bellum, the other part, a deep fissure between the vagal tuberosities ; 

 they communicate with each other by means of a narrow quadrangular 

 passage. 



The ventricle of optic lobe is simply the remains of the ventricle of 

 the corpora quadrigemina in foetus, and now part of the aqueduct of 

 Sylvius. 



The third ventricle, between the cerebral lobes and the optic lobe, 

 communicates behind with the last, and below with pituitary body by 

 means of the infundibulum ; above, it is closed in by the stalk of the 

 pineal gland. 



Origins of nerves : — 



The olfactory nerve arises from the olfactory lobe. 



The optic nerve arises by three roots, first from the tectum lobi 

 opici, second from the torus semicircularis, third from the hypoarium. 



The motor oculi arises from a ganglion beneath the floor of the 

 aqueeductus sylvii ; it partially decussates. 



The trochlearis arises from anterior part of the base of the cere- 

 bellum. 



The trifacial arises by three roots from beneath the anterior end of 

 the crura cerebelli ; its deep origin is from three distinct points ; first, 

 from cells beneath the floor of anterior part of the fourth ventricle ; 

 second, from the external lateral part of the spinal cord ; third, from 

 the central part of the vagal tuberosity. 



The abducens arises from two small ganglia in the ventral horn of 

 grey matter beneath the narrow part of the fourth ventricle. 



The acusticus arises from the lateral part of the medulla oblongata 

 in the region of the ganglion of the vagus. 



The glossopharyngeal has a. separate origin in mugil, in other 

 fishes it is a branch of the acusticus, in others again it is a branch of 

 the vagus ; here it arises from the grey matter covering the narrow 

 part of the fourth ventricle. 



The vagus arises by two roots, one from a ganglion beneath the floor 

 of posterior end of the fourth ventricle; the other from the cere- 

 bellum, and from the grey matter covering the narrow part of the 

 fourth ventricle. 



The first spinal nerve, although passing through a foramen in the 

 exoccipal, takes the place of the hypoglossal, rises by dorsal and 

 ventral roots, forms with the second spinal nerve the brachial plexus, 

 and supplies the region of the tongue. 



The spinal nerves have a ganglion on the dorsal root. 



The commissura ansulata, placed at the exit of the trochleares nerves, 

 is partly a longitudinal and partly a transverse commissure ; it first 

 appears on the external and lateral part of the medulla, opposite the 



