THE DIDELPHIA AND MONODELPHTA. 89 



with the scapula, and is not articulated with the sternum. All 

 have the so-called " marsupial " bones or cartilages ossifications, 

 or chondrifications, of the internal tendon of the external oblique 

 muscle of the abdomen and the females of almost all possess a 

 fold of the skin of the abdomen above the pubis, constituting a 

 " marsupium" or pouch, within which the young are nourished 

 and protected in their early, helpless condition. 



The oviducts open into vaginae, which are more or less com- 

 pletely divided into two separate passages. The testes of the 

 males are lodged in a scrotum, which is suspended in front of 

 the penis ; and the vasa deferentia open into a complete and 

 continuous urethra, which is also the passage by which the urine 

 escapes from the bladder, and is perfectly distinct from the pas- 

 sage for the fa3ces, though the anus and the termination of the 

 urethro-sexual canal are embraced by the same sphincter. 



The corpus callosum is comparatively small, and the anterior 

 commissure large, as in the Orniihodelphia. 



It is stated that the allantois of the embryo is arrested in its 

 development, and gives rise to no placenta. The umbilical sac 

 is said to acquire a large proportional size ; but whether it plays 

 the part of a placenta for the short period of intra-uterine life, 

 or not, is unknown. 



The young are born of very small size, and in a singularly 

 imperfect condition ; but being transferred to the marsupium, 

 and becoming attached to a long nipple, they are supplied with 

 milk until they are able to provide for themselves the milk 

 being, at first, forced into their mouths by the action of a muscle 

 spread over the mammary gland. 



In the MONODELPHIA, the angle of the lower jaw is not 

 inflected, and they may or may not be provided with teeth. 

 They never possess " marsupial " bones. The uterine dilatation 

 of the oviducts is always considerable, and whether they have 

 common or distinct apertures, the vagina is a single tube, 

 though it may be partially divided by a septum. The testes 

 may vary much in position ; but, if they are lodged in a scrotal 

 pouch, it is never pendulous by a narrow neck in front of the 

 penis, as in the Didelphia. 



