66o 



MANUAL OF ZOOLOGY. 



peculiar pouch formed by a folding of the integument of the abdomen. 

 This pouch is known as the " marsupium" and gives the name 

 to the order. Within the marsupium are contained the nipples, 

 which are of great length. Being for some time after their birth 

 extremely feeble, and unable to perform the act of suction, the 

 young within the pouch are nourished involuntarily, the mam- 

 mary glands being provided with special muscles which force 

 the milk into the mouths of the young ; while the windpipe is 

 prolonged up to the posterior nares, where it is embraced by 

 the soft palate, so that the food passes on each side of the 

 trachea, and there is no risk of suffocation. At a later stage 

 the young can suckle by their own exertions, and they leave 

 the pouch and return to it at will. In a few forms there is no 

 complete marsupium as above described ; but the structure of 

 the nipples is the same, and the young are carried about by 

 the mother, adhering to the lengthy teats. 



The so-called " marsupial bones " (fig. 360) doubtless serve 

 to support the marsupial pouch and its contained young, but 

 this cannot be their sole function, 

 since they occur in the male Marsu- 

 pials and also in the Monotremes, in 

 which there is no pouch. It is be- 

 lieved by Owen that the function of 

 the marsupial bones is to assist in 

 the action of the mammae and testes, 

 serving respectively as a fulcrum for 

 the muscle spread over the mam- 

 mary gland and for the cremaster. 



The oviducts open into vaginal 

 tubes which open into a urogenital 

 canal ; but this does not open into 

 a "cloaca," though embraced by a 

 sphincter muscle common to it and 

 to the rectum. In other words, the 

 vagina is separated wholly or in great 

 part into two distinct tubes, but these 

 open apart from the intestine. The 



. pelvis testes are llot abdominal throughout 



of a Kangaroo, showing the life as in the Monotremes, but are 



- " ^^ ^ & scrotum . ThiSj however, 



is placed in front of the penis, and 

 not beneath the pubic arch as in most Mammals. From this 

 unusual position of the scrotum, it is regarded by Owen as 

 being the same structure as the marsupial pouch of the female, 

 turned inside out. 



marsupial bones 



(;). (After 



