THE BRAIN 75 



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 

 fimb dated 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 



