538 THE ORGANS 



ascending tracts in the reticular formation. It gives rise to the bundle of 

 Vicq d'Azyr (mammillo-thalamic tract) to the dorsal nucleus of the thalamus, 

 and mammillo-tegmental fibres to the nucleus of Gudden (Fig. 382) and red 

 nucleus. The fibres entering the mammillary body from the fillet and other 

 ascending tracts, together with the mammillo-tegmental tract, constitute its 

 peduncle. It is not improbable that the mammillary body is a link in the 

 afferent gustatory path (p. 482, II). (See also Endbrain.) 



On the right is seen the posterior part of the nucleus lenticularis of the corpus 

 striatum. 



The Endbrain or Telencephalon. 



The endbrain consists of pallium (dorsal expanded part), corpus 

 straitum, and rhinencephalon. Two principal parts of the pallium 

 may be distinguished; the olfactory pallium or rhinopallium (archi- 

 pallium), including principally the cornu ammonis and gyrus denta- 

 tus; and the neopallium including the greater part of the cerebral 

 hemispheres. 



The rhinencephalon^ includes the olfactory nerves and bulb, the 

 trigonum olfactorium, the tuberculum olfactorium or anterior perfor- 

 ated space, and the gyrus hippocampi, in part at least (pyriform lobe). 

 The olfactory nerve is composed of axones of cells in the olfactory 

 mucous membrane which terminate in the olfactory bulb. They there 

 form synapses with the dendrites of the mitral cells, the axones of 

 which constitute the secondary tract, part of which decussates in 

 the pars olfactoria of the anterior cerebral commissure. A secondary 

 tract ("lateral root") proceeds, with tertiary tracts, to the cortex of 

 the gyrus hippocampi and thence to the cornu ammonis. Efferent 

 axones of cornu ammonis cells are collected in the fimbria and descend 

 by the fornix to the mammillary body, the further caudal connec- 

 tions of which have been described (p. 537J. Fibres of the fimbria 

 also cross, forming the commissure of the fornix (olfactory pallial 

 commissure). Secondary olfactory tracts also pass to the trigonum, 

 whence tertiary neurones pass as the stria medullaris to the ganglion 

 habenulas (see p. 536 and Fig. 359). The principal commissure 

 of the rhinencephalon is the anterior cerebral commissure. 



The corpus striatum consists of the nucleus caudatus and nucleus 

 lenticularis, the connections and significance of which are obscure. 

 They receive collaterals from the descending pallial fibres which 

 pass by them and also apparently send out fibres to join the latter. 

 They also have connections with rhinencephalon and thalamus. 



' The term rhinencephalon is often used to include also the olfactory pallium. 



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