566 ZOOLOGY. 
opens in the female immediately below the anus, but in the 
male enters the penis. 
The ovary (Ov) is small and is placed near the open end 
of the oviduct or Fallopian tube, which can be seen in the 
figure extending alongside the rectum above the bladder. 
The two oviducts (Ovd) unite posteriorly to form the uterus. 
(Ut). 
Fig. 492, II., isa median longitudinal section of the brain. 
The spinal cord passes into the medulla oblongata (M), over 
which lies the large cerebellum (Cb), and the small corpora 
quadrigemina (Q). In front is the large cerebrum (C) and 
the small olfactory lobe (Z). Fig. 492, III., is a diagram of 
the eye (see explanation of the figure). 
By carrying the dissection further, the student will be able 
to examine the tongue with its papille ; the epiglottis at. 
the back of the mouth in front of the trachea; the larynx, 
wu peculiarly modified portion of the trachea in the neck, 
with two elastic bands stretched across its interior; the 
bands or vocal cords may be set in vibration by a blast of 
air from the lungs. The heart may also be dissected fur- 
ther to find the origin of the pulmonary vessels, and to 
make out the four divisions or chambers. (Minot.) 
The eggs of mammals are exceedingly minute, partly owing 
to the small quantity of yolk in them; the eggs of the few 
which have been examined are about a quarter of a milli- 
metre (+4;—z4y inch) in diameter. In the duckbill the egg 
is large and with more yolk, like those of birds, being about 
five millimetres in diameter. Mammals are divided into 
non-placentals and placentals, according as the embryos are 
surrounded or not with a placenta or ‘‘ after-birth.’? This 
organ is a development of the allantois, serving as a means 
chiefly of nutrition, being filled with blood-vessels leading 
from the walls of the womb of the parent, and also acting 
as an organ of respiration, and to carry off the effete pro- 
ducts by means of the maternal circulation. 
Mammals may be born helpless and only partly developed, 
as in the Marsupials; or capaole of locomotion and sucking 
milk, as in the calf or colt; or helpless for many months, 
as in human infants. The changes in the form of the body 
after birth are much less, on the whole, than in the birds. 
The sexes differ externally in size and ornamentation. 
