THE BRAIN. 315 



which is motor, the posterior sensory ; and between these a Nerves of the 

 dark vesicular deposit, the locus niger, which is continuous ^^^ifdsre^ 

 between the vesicular matter in the spinal cord and that of spectiveiy. 

 the thalamus and corpus striatum. From the lowest extremity of the 

 cord to these great ganglia there is, therefore, an unbroken vesicular 

 channel. In its progress onward to the corpus striatum, the anterior 

 strand yields roots of the spinal accessory, hypoglossal, facial, abducens, 

 the small root of the fifth, the trochlearis, and the oculo-motor nerves. 

 If there were no other proof of the motor character of this strand, the 

 motor property of all these nerves would be sufficient to determine it. 

 In like manner, the posterior strand yields the pneumogastric, the glosso- 

 pharyngeal, and the sensory root of the fifth, from the sensory functions 

 of which its sensory character is established. 



The layer of vesicular matter which is found upon the cerebral convo- 

 lutions, and which is doubtless the seat of the higher intel- Relation of the 

 lectual qualities, has therefore no communication with the ^roftoe hem- 

 vesicular matter of the spinal axis, by contact or continua- ispheres. 

 tion, but only through the intervention of fibres which radiate upon it in 

 all directions from the thalamus and striatum, or rather through some 

 which radiate from the great sensory centre, the thalamus, to the periph- 

 ery of the cerebrum, and others which converge from that periphery to 

 the great motor centre, the striatum. If the diameter of these fibres be 

 assumed to be 10 ooo of an inch, there must be many millions of them 

 in the aggregate. The vesicular matter of the hemisphere is arranged 

 on the superficies instead of centrally, on account of the necessities of 

 their structure and condition of activity, for thereby a great surface is 

 obtained, which is further increased by the artifice of convolutions, a ve- 

 sicular surface which, counting in that of the cerebellum, has been esti- 

 mated at 670 square inches, and blood can be copiously supplied and 

 freely removed. 



But the thalamus and striatum are only two of a chain of ganglia be- 

 neath the cerebral hemispheres. Anteriorly we find the ol- Gapglia at the 

 factive ganglia, or bulbs of the olfactory nerves, which are base of the 

 seated upon peduncles, though their character is manifest from 

 the gray matter they contain. Behind these are the tubercula quadri- 

 gemina, to which the optic nerves run, and which are therefore their gan- 

 glionic centres. What answers to the auditory ganglion is lodged at a 

 distance back, at the fourth ventricle, and the gustatory ganglion is in 

 the medulla oblongata. These are the ganglia of special sense, and to 

 be regarded as subordinate to the thalamus, 'which is their common 

 register. 



All these parts are commissured with one another, and with their fel- 

 lows of the opposite half of the brain. Indeed, so likewise are all its 



