II THE BRAIN 7% 
and is a piece of evidence in favour of the high position of the 
mammals. 
The oviducal apparatus of the mammal is more specialised 
than that of lower vertebrates. It is most simple, as might be 
imagined, in the egg-laying Monotremes, where, indeed, it is on 
the same level as that of reptiles. But in the Eutheria the 
fimbriated mouth of the oviduct passes into a narrow and wind- 
ing tube, the Fallopian tube; this widens into a uterus, and the 
two uteri combine into a single tube in the higher forms. They 
are called the Monodelphia on this account. In the Marsupials 
the uteri are distinct though they often join above, and from 
this junction depends a median “uterus.” After the uterus or 
the uteri follows in every case a single vagina. 
The testes of the Mammalia, like those of other vertebrates, 
occupy primitively a position within the body cavity precisely 
corresponding to that of the ovaries. And in the lowly-organised 
Monotremata, and some other forms, such as the Whales, they 
retain that primitive position within the body. It is, however, 
distinctive of the Mammalia as opposed to lower vertebrates that 
the testes descend later into a scrotum, which is simply a pro- 
trusion of the skin of the body surrounded by muscles, and, of 
course, containing a section of the body cavity in which lie the 
testes. The penis of the Mammalia, represented by the clitoris 
and associated structures in the female, is of a structure entirely 
peculiar to this group. 
The Brain.—Inasmuch as Professor Wiedersheim has said 
with perfect truth that “the brain of the extinct Ungulate 
Dinoceras shows so striking a likeness to that of a lizard that 
one would be compelled to explain it as that of a lizard without 
a knowledge of the skeleton,’ it is clear that to define the 
mammalian brain is a difficult matter. The existing Mammalia, 
however, all possess brains which can be readily distinguished 
from those of vertebrates lying lower in the scale. They are 
of relatively large size, brought about mainly by the dimensions 
of the cerebral hemispheres, which have an importance in this 
class of vertebrates that they have not elsewhere. Coupled 
with this large size of the hemispheres is a more elaborate 
system of transverse commissures uniting the two; and this 
culminates in the higher Mammalia, where the corpus callosum 
attains a large size and great physiological importance. <A 
