370 BRAIN OF MAN. 



pass from each hemisphere to its fellow through the corpus 

 callosum, whilst others again bring the different convolutions 

 of the same hemisphere into mutual connexion. The hemi- 

 spheres are (so to speak) wrapped round the collection of 

 Sensory Ganglia in which the spinal cord may be said to ter- 

 minate at its upper end, in such a manner as to leave two 

 cavities, one on either side, which are called the lateral ven- 

 tricles. 1 The Sensory Ganglia are so small relatively to the 

 Cerebrum, that they would scarcely attract notice as inde- 

 pendent centres, if they were not carefully compared with the 

 ganglionic centres corresponding to them among the lower 

 animals. The olfactory ganglia are mere bulbous enlarge- 

 ments upon the cords (1), which, though commonly termed the 

 olfactory nerves, are really (as in the Shark, 453) footstalks 

 connecting these ganglia with the rest of the series ; it being 

 from these ganglia that the true olfactive nerves are given off 

 ( 506). The optic ganglia, g, only in part represent the 

 optic lobes of Fishes ; the function of the latter being shared 

 by two large masses termed the thalami optici, which form 

 the hinder part of the floor of the lateral ventricles, and 

 which also seem to participate in the sense of touch, as the 

 sensory columns of the spinal cord may be traced up to them. 

 This close connexion of the sensorial centres of Sight and 

 Touch is just what we might anticipate from the continual 

 co-operation of these two senses ( 556, 557). In front of 

 the optic thalami is another pair of large ganglionic masses, 

 termed the corpora striata, which is in the like close relation 

 with the motor columns of the spinal cord ; and it is chiefly 

 from them and from the thalami optici, that the fibres pro- 

 ceeding to the surface of the Cerebral hemispheres radiate. 

 The Cerebellum, which has no direct communication with the 

 Cerebrum, but possesses independent connexions of its own 

 with the upper part of the spinal cord, has its grey or vesicular 

 and its white or fibrous substance so peculiarly disposed, as 

 to present in section the appearance delineated at d, which 

 is termed the arbor vita?, or tree of life. 



459. Of the nerves given off within the skull (figs. 1 9 6, 1 97), 



1 There are other ventricles, which are merely spaces left on the 

 middle plane by the imperfect coalescence of the two lateral columns 

 of the nervous axis, like the openings formed by the divergence of the 

 two halves of the nervous cord in Insects (fig. 188). 



