9 o 4 THE CENTRAL NERVOUS SYSTEM 



afferent paths to the cortex with which the thalami are specially related 

 as centres of relay. The fibres of the upper fillet carrying afferent im- 

 pulses up from the opposite posterior column of the cord to the cere- 

 brum end in the grey matter of the thalamus, as does the central path 

 of the afferent fibres of the opposite fifth nerve. The posterior portion 

 of the thalamus, or pulvinar, forms part of the central visual apparatus ; 

 for (a) it is found to be undeveloped in animals from which the eyeballs 

 have been removed soon after birth; (b) a portion of the optic tract is 

 certainly connected with it; (c] in some cases of atrophy of the occipital 

 cortex, which, as we shall see, is undoubtedly a central area for visual 

 sensations, atrophy of the pulvinar has also been noticed; (d) a lesion 

 of the pulvinar may give rise to hemianopia (p. 894). 



Haemorrhage into the caudate or lenticular nucleus of the corpus 

 ftriaium often causes hemiplegia, but this is frequently due to implica- 

 tion of the internal capsule. It is said, however, that lesions presumably 

 confined to the lenticular nucleus cause paralysis or paresis of the limbs 

 or face, which is less severe than that produced by lesions in the internal 

 capsule. Experimental lesions in dogs and rabbits are stated to be 

 followed by disturbances of the heat-regulating mechanism and rise of 

 temperature. 



Certain structures belonging to the primary fore-brain which have 

 now lost some or all of their functional importance may nevertheless be 

 mentioned as milestones in the march of development. The pineal 

 body is made up of the vestiges of the unpaired mesial eye of such 

 animals as the ancient labyrinthodonts, which resembled the eye of 

 invertebrates in having the retinal rods directed towards the cavity 

 instead of towards the circumference of the eyeball. In many living 

 forms, especially in certain lizards, this pineal or parietal eye is found 

 in a more perfect condition, though covered by a thin membrane. The 

 ganglia habenulce, two small collections of nerve-cells, one of which is 

 situated at the posterior part of each thalamus, are supposed by some 

 authorities to represent the optic ganglia of this cyclopean eye. They 

 are less prominent in man than in many of the lower animals. The 

 infundibulum is probably what remains of the gullet of the ancestors 

 of the vertebrates. The pituitary body is in a different category. It 

 is now known that, far from being a useless vestigial remnant, it has a 

 highly important function (p. 644). It consists of two portions, the 

 anterior lobe, or hypophysis, derived from the buccal cavity, the pos- 

 terior lobe, or infundibular body, from the primary fore-brain. 



Functions of the Cerebellum. The elaborate pattern of the arbor 

 vitae, the appearance given by the branched laminae in a section 

 of the cerebellum, excited the speculation of the old anatomists. 

 A structure so marvellous must be matched, they thought, with 

 functions as unique. At a time when the discoveries of Galvani 

 and Volta were fresh, and the world ran mad on electricity, the 

 hypothesis of Rolando, that ' nerve-force ' was generated by the 

 lamellae of the cerebellum as electrical energy is generated by the 

 plates of the voltaic pile, ridiculous as it now appears, was not 

 unnatural. The speculation of Gall, who connected the cerebellum 

 with the development of sexual emotions and the action of the 

 generative mechanisms, was based on no fact. It has been definitely 

 disproved by the observations of Luciani, who found that a bitch 

 deprived of its cerebellum showed all the phenomena of heat or 





