42 NERVOUS STSTEM: AND GENERAL SENSATION. 



A horizontal section shows that the quantity of white suo- 

 stance considerably exceeds that of the gray. The cerebellum 

 is connected with the brain and spinal cord by three pairs of 

 medullary fasciculi. From the interior of the lobes two fasci- 

 culi (processus e cerebello ad testes) pass forwards and up- 

 wards to the optic lobes, g. In their ascent they converge, 

 and are connected by a fold of neurine, called the valve of 

 Vieussens.* Two round white processes, corpora restiformia, 

 pass obliquely downwards, and are continued into the posterior 

 columns of the medulla oblongata. The largest of the fasci- 

 culi are the crura cerebelli, which incline forwards and in- 

 wards, and become continuous with the fibres of the pons 

 Varolii.f This bridge of neurine bears the same relation to 

 the cerebellum that the corpus callosum does to the cerebrum ; 

 it is composed of converging fibres, and may therefore be re- 

 garded as the ccrebellar commissure. 



[ 88. THE OPTIC LOBES. When we raise the posterior 

 lobes of the brain, we observe between this organ and the 

 cerebellum four small round eminences, placed in pairs on 

 each side of the median line (fig. 20, g), upon the superior 

 surface of the medullary prolongations, which ascend from the 

 spinal cord to expand in the cerebrum ; these are the optic 

 lobes, which are developed in a direct ratio with the volume of 

 the optic nerves. 



[ 89. THE SPINAL CORD is that division of the cerebro- 

 spinal system, inclosed in all the vertebrata, within the 

 spinal canal. In man it reaches from the lower border of the 

 pons Varolii to the first or second lumbar vertebra, whilst in 

 the foetus it extends throughout the whole length of the spinal 

 canal ; in this respect representing the permanent condition ot 

 the spinal cord in reptiles and fishes. We observe three dis- 

 tinct enlargements of the cord, in different parts of its course. 

 The cranial swelling, or medulla oblongata, exhibits a conside- 

 rable expansion, near the margin of the pons, which diminishes 

 before entering the foramen magnum : on its lateral parts are 

 three eminences, the pyramidal, olivary, and restiform bodies. 

 The second enlargement corresponds to the interval between 

 the third and fifth cervical vertebrae ; the third, to that be- 



* Vieussens, a great anatomist ; his Neurographia Universalis was pub- 

 lished at Lyons in 1685. 



t In honour of a celebrated anatomist of the sixteenth century, Varoli. 



