482 MANUAL OF ZOOLOGY. 



There are two ovaries in all Mammals, and the oviducts are 

 known as the " Fallopian tubes." Each oviduct dilates on its 

 way to the surface into a uterine cavity, which opens into the 

 vagina. In the Monotremes and Marsupials this primitive 

 condition is retained throughout life, the uterus remaining double, 

 and opening by two apertures into the cloaca or vagina. In 

 most cases this condition is so far modified in the adult, that 

 the two uteri have coalesced inferiorly, so as to have only a 

 single opening into the vagina, whilst they separate into two 

 horns or " cornua" superiorly. Only in the Monkeys and in 

 Man have the two uteri completely coalesced to form a com- 

 pletely single cavity, into the " fundus" of which the Fallopian 

 tubes open. In male Mammals there are always two testes 

 present. In many Mammals the testes are permanently 

 retained in the abdominal cavity and there is no scrotum. 

 This is the case in the Monotremes, the Elephants, all the 

 Cetacea, and many of the Edentata. Mostly, however, the 

 testes at an early period of life are transferred from the ab- 

 domen to a pouch of integument called the " scrotum." 

 Usually the scrotum is placed beneath the pubic arch and 

 behind the penis, but this position is reversed in the Marsupials. 



Mammary glands are present in all Mammals, and they are 

 regarded by Huxley as an extreme modification of the cutane- 

 ous sebaceous glands. In the male Mammals the mammary 

 glands are present, but, under all ordinary circumstances, they 

 remain functionally useless and undeveloped. Considerable 

 differences obtain as to the number and position of the mam- 

 mary glands in different cases ; but they are always placed on 

 the inferior surface of the body, and their ducts in the great 

 majority of cases open collectively upon a common elevation 

 the "teat" or "nipple." In the Monotremata, however, 

 there are no nipples, the ducts of the mammary glands open- 

 ing either into a pouch of the integument (Echidna) or upon a 

 flat surface (Ornithorhynchus). 



The young Mammal is nourished for a longer or shorter 

 time by the milk secreted by the mammary glands of the 

 mother. In ordinary cases the milk is obtained by voluntary 

 suction on the part of the young animal ; but in the Marsupials 

 the young are at first unable to suck for themselves, and the 

 milk is forced out of the gland by the contractions of a special 

 muscle. 



The nervous system of Mammals is chiefly remarkable for 

 the great proportionate development of the cerebral mass as 

 compared with the size of the spinal cord. In the higher 

 Mammals, again, the hemispheres of the cerebrum are much 



