REPRODUCTIVE ORGANS 75 
spongiosum not being present. In many Marsupials the glans penis 
is bifurcated. In most Primates, Carnivora, Rodentia, Insectivora, 
and Chiroptera, but in no other orders, an os penis is present. 
Ovaries and Oviduct.—In the female, the ovaries permanently retain 
their original abdominal position, or only descend a short distance 
into the pelvis. They are of comparatively smaller size than in 
other vertebrates, have a definite flattened oval form, and are 
enclosed in a more or less firm “tunica albigenia.” The oviduct 
has a trumpet-like, and usually fimbriated abdominal aperture, and 
is more or less differentiated into three portions :—(1) a contracted 
upper part, called in Man and the higher mammals the “ Fallopian 
tube”; (2) an expanded part with muscular walls, in which the 
ovum undergoes the changes by which it is developed into the 
foetus, called the “uterus”; (3) a canal, the “vagina,” separated 
from the last by a valvular aperture, and terminating in the urino- 
genital canal, or common urinal and genital passage, which in 
higher mammals is so short as scarcely to be distinct from the vagina. 
The complete distinction of the oviducts of the two sides through- 
out their whole length, found in all lower vertebrates, only occurs 
in this class in Monotremes ; a prevailing mammalian characteristic 
being their more or less perfect coalescence in the middle line to form 
a single median canal. In the Marsupials this union only includes 
the lower part of the vagina ; but in most Placentals it extends to the 
whole vagina and a certain portion of the uterus, which cavity is 
then described as “bicornuate.” In the higher mammals, as in 
Man, and also in some of the Edentates, the whole of the uterus is 
single, the contracted upper portion of the oviducts or Fallopian 
tubes, as they are then called, entering its upper lateral angles by 
small apertures. In certain lower forms the urino-genital canal 
opens with the termination of the rectum into a common cloaca, 
as in other vertebrates; but it is characteristic of the majority 
of the class that the two orifices are more or less distinct exter- 
nally. 
Mammary Glands. —Mammary glands secreting the milk by 
which the young are nourished during the first portion of their 
existence after birth, are present in both sexes in all mammals, 
though usually only functional in the female. In the Monotremes 
alone their orifices are mere scattered pores in the skin, but in all 
other forms they are situated upon the end of conical elevations, 
called mammille or teats, which, taken into the mouth of the 
young animal, facilitate the process of sucking. These are always 
placed in pairs upon some part of the ventral surface of the body, 
but vary greatly in number and position in different groups. In 
the Cetacea, where the prolonged action of sucking would be incom- 
patible with their subaqueous life, the ducts of the glands are 
dilated into large reservoirs from which the contents are injected 
