48 Jt)UKNAI. OF Co.Ml'AKATl\J': NE^U()I,<)(.^ . 



This tuber is usually absent. In such cases the dorsal tuber 

 may be mistaken for it. 



]'ciitro-mcdia!/ tuber (Plate V, Figs. 1, 7, 9, 13). — This 

 is a convex swelling, the sides of which slope gently in all 

 directions. It lies upon the mesal half of the prosencephalon 

 between the rhinencephalon and the optic chiasm. In some 

 species (Pate V, Figs, i, 9, 13) this tuber is quite large, in 

 others (Plate \ , Fig. 7) it is small, in still others it is 

 apparently absent. 



^'entro-latcral tuber (Plate \', Figs, i, 4, 7. 9, 13). — This 

 tuber is almost universally present. It is usually the largest 

 tuber of the brain and seems to be the homologue of the 

 pyriform tuber of mammals. It is a relatively large swelling, 

 which is situated at the caudo-lateral angle of the ventral 

 surface of the cerebral hemisphere. Laterad, caudad, and 

 mesad, the surface of this tuber is strongly convex; cephalad, 

 the surface is slightly convex. This surface of the tuber 

 slopes gradually towards the surface of the prosencephalon. 

 Its length is usually a little more than one-third that of the 

 prosencephalon v/hile its breadth is usually a little more than 

 half the breadth of the hemisphere. 



Innotninate tuber. — This is a small, slightly developed 

 tuber, which I have occasionally noticed. It is situated 

 somewhat mesad to the ventro-lateral tuber and is partly 

 covered by the optic lobe. Its small size and the irregularity 

 of its presence cast some doubt upon the propriety of recog- 

 nizing it as a distinct tuber. 



EXI-r.AN AllOX OI' TABLE II (sEE I'. 8o). 



" Length" is a contraction for " Ratio of the length of the prosni- 

 cephaton to the length of the brain." 



"Breadth" is a contraction for " Ratio of the greatest breadth of 

 the proseticeplialon to the length of the brain." 



"Depth" is a contraction for "Ratio of the greatest depth of the 

 proseticeflialflu to the length of the brain." 



All ratios are expressed in hundredths of the length of 

 the brain. 



'i'he length of the brain is the distance from the cephalic extremity 



