256 



THE BRAIN OF QUADRUPEDS AND 



are more or less deeply indented in the transverse direc- 

 tion, by a depression or groove which thus divides them 

 into four rounded swellings, answering to what, in higher 

 animals and in Man, are known as the ' Corpora Quadri- 

 gemina.' The cavity existing within them in lower Verte- 

 brates now becomes reduced to a mere passage between 

 the third and fourth Ventricles. 



(2.) A great transverse commissure, connecting the 

 Cerebral Lobes with one another, appears as a rudi- 



FIG. 69. Brain of the Horse, outer surface. (Solly, after Leuret.) e, Olfactory 

 lobe ; h, hippocampal lobe, or ' processus pyriformis. 1, 2, 3, Lobes of the Cere- 

 bellum, o, Optic nerve ; m, motor occuli ; p, fom*th nerve ; t, fifth nerve ; u, sixth 

 nerve ; /, facial nerve ; I, auditory ; g, glosso-pharyngeal ; v r vagus ; 8, spinal- 

 accessory ; n, hypoglossal nerve, x, Pons Varolii 



mentary structure in lower Quadrupeds and gradually 

 increases in size in higher representatives of this class. 

 It is known as the Corpus Callosum. This commissure 

 principally connects the upper parts of the Cerebral 

 Lobes, and soon comes to form the roof of the two great 

 ' lateral ventricles.' 



(3.) A double commissure, known as the Pornix, appears 

 and gradually becomes more developed, as another boundary 

 of the * lateral ventricles.' Long erroneously described 



