274 THE BRAIN OF QUADRUPEDS AND 



figures show a more developed form of the Corpus Cal- 

 losum in the Horse (fig. 72), in the Dolphin (fig. 85), and 

 in the Dog (fig. 87). 



The Corpus Callosum stretches across from one Cere- 

 bral Hemisphere to the other ; its fibres constitute the 

 roof of each Lateral Ventricle, and thence diverge to many 

 parts of the surface grey matter of each Hemisphere. 

 Similar cortical areas on the two sides are thus brought 

 into functional relation with one another. It has, therefore, 

 a wider kind of office, though identical in nature to that 

 performed by the Anterior Commissure. It is an error, 

 however, to place these structures in the same category 

 with the Fornix, as many of the older anatomists and 

 even some modern writers have done — since this latter 

 commissure serves to unite difi'erent regions of the same 

 Hemisphere, rather than similar regions of the two 

 Hemispheres with one another. 



The mode in which the Corpus Callosum and the Fornix 

 are united posteriorly by the * psalterial fibres,' and the 

 way in which the same two bodies recede from one another 

 anteriorly, and thus contribute to the formation of the 

 Fifth Ventricle, has been previously described {see also 

 fig. 72). 



Any one wishing to obtain more distinct notions as to 

 the varying developments and relations of these several 

 Commissures, should consult the admirable figures 

 given by Flower,* illustrating the relative size and dis- 

 tribution of these parts in the Sheep, Eabbit, Sloth, and 

 Hedgehog, as compared with what obtains among certain 

 Marsupials and Monotremes. 



* Philosoph. Traus. 1865, PI. xxxvii. aud xxxYiii. 



