THE BRAIN OF MACROSCELIDES. 44:7 
the upper surface of this commissure, just as happens also in the 
Metatheria; and yet, high up near the dorsal margin of the 
hemisphere, there is an undoubted corpus callosum. The shape 
of this body is no less peculiar than its extraordinary position. 
It is exceedingly large and thin, and exhibits a state of affairs 
which is almost unknown beyond the limits of the Primates. 
It is, moreover, provided with a plump splenium and a long 
hook-like genu ending in a sharp rostrum. 
Both in shape, size, and position this corpus callosum (c.e.) is 
as unlike the primitive generalized condition of the corpus 
callosum, such as is found in Erinaceus, as it is possible to 
imagine. 
The most primitive form of corpus callosum is exhibited in 
the brain of many small Bats such as Myctophilus * ; but whether 
as the persistence of the original condition or as a secondary 
reversion to it, does not especially concern us now. In 
Hrinaceus~ the evoiution of the corpus callosum is carried only 
shghtly further. 
In many small Insectivores like Hemicentetes, Oryzoryctes =, 
and others, a similar state of affairs is found. In Gymnura ¢ and 
Talpa the corpus callosum is larger, but the condition is essentially 
thesame. In Chrysochloris{;there is an extraordinary elongation 
of the corpus cailosum, such as we do not find in other small 
Insectivores, nor in the Edentate Chlamydophorus, which in this 
respect resembles Hrinacews much more closely than does the 
Golden Mole. 
But even in Chrysochloris the corpus callosum is not nearly 
so long as it is in Macroscelides, while in the former it has 
the primitive straight form. Thus while MWacroscelides has the 
most specialized form of corpus callosum of all Insectivores, 
its psalterium retains the peculiar crescentic form found else- 
where only in the Marsupialia. 
In all other mammals with a corpus callosum the growth of 
the latter modifies the shape of the psalterium by pulling it 
* Cf. “The Origin of the Corpus Callosum,” Trans. Linn. Soe., ser, II. Zool. 
vol. vii. pt. 3 (1897). 
+ Cf. “The Relation of the Fornix to the Margin of the Cerebral Cortex,” 
Journ, Anat. & Phys. vol. xxxii. 1898, p. 45. 
{ For the brain of Gymnura I am indebted to Dr. Charles Hose ; for that of 
Hemicentetes and Oryzoryctes to Dr. Forsyth Major ; and for that of Chryso- 
chloris to Dr. Broom. 
