24 Fierp Museum or Narurat History — Zoooey, Vor. XI. 
membranes of the uterus, and through this placenta the embryo is 
nourished. 
In all female mammals, cxcept the Monotremes, the intestinal 
and genital openings are separate, but in the latter they open into 
the cloaca, as in birds. 
Mammary Glands — These glands secrete milk by which the young are 
nourished and are present in both sexes in all mammals, but are 
usually only functional in the female. 
In all except the Monotremes their orifices are situated upon the 
end of conical elevations called mammile, or teats, which are taken 
into the mouth of the young animal. In the Whales the glands are 
unusually developed and a quantity of milk is injected into the 
mouth of the young by muscular contraction. In the Monotremes 
the teats are lacking, the ducts of the mammary glands opening 
through pore-like orifices in the skin. In addition to a number of 
other peculiar characters, these strange mammals are claimed to be 
oviparous, the eggs resembling in development those of a reptile. 
NERVOUS SYSTEM AND ORGANS OF SENSE. 
The Brain — The brain is contained in the cavity of the skull. The 
greater portion is called the cerebrum, a much smaller portion at the 
back of the skull cavity is known as the cerebellum; and the com- 
mencement of the spinal marrow, as the medulla oblongata. The 
brain of a mammal differs from that of other vertebrates in having 
the two hemispheres of the cerebellum united by a commissure (pons 
varolit) and the cerebral hemispheres more or less connected by an 
anterior and a superior transverse commissure, the corpus collosum 
of anatomical text books. In most mammals the brain is more or 
less convoluted, highly so in Man, varying in degree in many, or not 
at all as in some of the Marmosets (Ha pale). 
Spinal Cord — The main nerve axis of the body passing through the 
vertebree from head to tail, but which it is unnecessary to discuss 
here. 
The Sense of Touch— An increased supply of nerves and blood-vessels 
to a part of the skin renders it more sensitive and susceptible to 
what is called the sense of touch. Dermal susceptibility for this 
reason differs in various parts of the body. For example, in Man 
the ends of the fingers, from being supplied abundantly with pencil- 
late plexuses of nerves, are much more sensitive than portions of the 
arm or back. The lips and tongue are still more so, the latter 
usually being capable of distinguishing distinct sensations when 
touched by the points of a pair of dividers when separated only |}, 
