NERVOUS SYSTEM. VERTEBRATA. 



345 



The lateral wall is deeply invaginated into the cavity 

 of this ventricle (fig. 200), so as to produce a great ver- 

 tical furrow on the surface (fig. 198). This " complete " 

 sulcus is of a very different nature to the Sylvian fissure 

 of any mammal of other Orders. In some brains this 

 sulcus appears to bifurcate both above and below (fig. 198), 

 but in other cases the posterior limb at the upper extremity 

 may be a separate sulcus (?suprasylvian); and sometimes 

 also the postero-inferior limb is wanting. 



Neither of these lower limbs represents the rhinal fissure, 

 as Beddard believes, because the situation of the rhinal 

 fissure can be readily determined at a lower level, although 



Fig. 199. (xf.) 



SULC/'SPLEN 1 



CORP. CALL. 



PSAL.^ 



GEN.... 



,A 

 I 



OLF. BULB. ', 



GANB.HAB. 



CORP. QUAD. 



CER. 



fp>r 



^""^-^il^ ^S SOFT COMM. 

 COMM. ANT. OPT. CH1ASMA. 



the fissure itself is almost wholly aborted. The inferior 

 bifurcation ought rather to be compared to the limiting 

 furrows of the Sylvian depressed area, which are such 

 constant appendages of the ventral extremity of the 

 " Sylvian fissure " of the Ungulata. Their nearest 

 analogues are therefore the two sulci called " ectosylvian " 

 in the Ungulata. 



The small olfactory bulb, the flattened ribbon-like olfac- 

 tory peduncle, and the ill-defined tuberculum olfactorium 

 and pyriform lobe present no unusual features beyond 

 their smallness (as a result of the aquatic habits of the 

 Manatee) and the abortion of their boundary, the rhinal 

 fissure. The hippocampus also presents the characteristic 



