II ORRIC LOBES iI 
merely selected cases, which do not indicate a wide applicability 
of such a generalisation. Thus it is true that the brain of a Man 
is more elaborate in its furrows and conyolutions than is that of 
a Cat. The real fact of the matter is, that the complexity of the 
brain from this point of view increases with the size of the animal 
within the group. 
The Gorilla and the Chimpanzee have a more furrowed brain 
than has the lttle Marmoset; the Bear a more complicated 
brain than the Weasel, etc. The most highly-convoluted brains 
of all mammals are those of the Elephants, and there does not 
Fic. 50.—Lepus cuniculus. Longitudinal vertical section of the brain. (Nat. size.) 
a.co, Anterior commissure ; 6.70, body of the fornix ; cb, cerebellum, showing arbor 
vitae ; ¢.¢, crus cerebri; ¢./1, parencephalon or cerebral hemisphere ; ¢.h?, temporal 
lobe : ¢.ma, corpus mammillare ; cp.cl, corpus callosum ; fm, foramen of Monro ; 
inf, infundibulum ; @.4, lamina terminalis; Zy, lyra; m.co, middle commissure ; 
m.o, medulla oblongata ; o.ch, optic chiasma; o0./!, 0./?, corpora quadrigemina or 
optic lobes ; off, olfactory lobe ; p.co, posterior commissure ; pd.pn, peduncle of the 
pineal “gland,” pn; p.fo, anterior pillar of the fornix ; pty, pituitary body ; pv.a, 
pons Varolii; sp./du, septum lucidum ; v4, fourth ventricle ; v/.ip, velum interposi- 
tum ; v.vn, valve of Vieussens ; Z/, optic nerve. (From Parker’s Zootonvy.) 
seem in the Ungulates to be so marked a relation between size 
and abundance of fissures as there is among other mammals. 
A regular plan of the fissures can be detected with certainty 
for each group considered by itself; but it is not so easy to 
homologise the details of arrangement from group to group. 
This is so far in accord with the view that the existing groups 
of mammals have diverged from each other ab initio. 
Another marked characteristic of the mammalian as opposed 
to other brains is the relatively small importance in size and yet 
the fourfold nature of the optic lobes. What was the case with 
the optic lobes of the early Ungulates is difficult to understand, 
on account of the fact that the casts are necessarily imperfect. 
