352 ANATOMY OF THE RABBIT 



striae) composed of fibres from olfactory correlation cen- 

 tres. The habenulae receive impulses from various olfac- 

 tory regions of the cerebral hemisphere and tactile and 

 other related sensory impulses which they correlate with 

 them, sending resultant excitation impulses to motor cen- 

 tres, especially those concerned with feeding. 



(h) The posterior commissure (commissura posterior) crosses 

 the posterior portion of the roof immediately behind and 

 below the habenular commissure, so that only its rostral 

 edge is visible from above, as indicated in Fig. 116. It is 

 a composite structure which, like other commissures, con- 

 nects parts on the two sides of the brain. 



(i) The very thick masses of nervous tissue which form the 

 lateral walls of the third ventricle are the thalami. They 

 are broadly connected by the intermediate mass (massa 

 intermedia) or middle commissure, which may be seen 

 from the dorsal surface crossing and largely filling up 

 the ventricular cavity. This is not a true commissure 

 (a band of nerve fibres connecting corresponding structures 

 bilaterally), but is simply a fusion of the grey matter lining 

 the walls of the ventricle, brought about by the increased 

 thickness of the thalami. The latter contain various reflex 

 centres and serve especially as a relay station through 

 which pass all impulses proceeding to the cerebral hemis- 

 phere, except the olfactory ones. 



(j) On either side, lateral to the habenula, the dorsal portion 

 of the thalamus forms a low, somewhat oval projection, 

 the lateral thalamic tubercle. This swelling represents 

 superficially a mass of grey matter through which pass 

 most of the sensory impulses to the hemispheres from 

 lower parts of the nervous system other than visual and 

 auditory. 



The anterior tubercle of the thalamus is a faint elevation 

 of very small dimensions lying in the angle enclosed be- 

 tween the lateral tubercle and the anterior portion of the 

 aperture of the third ventricle. It also is a relay station for 

 impulses to the cerebral cortex, in this case mainly ones 

 coming from olfacto-visceral correlation centres. 



