MARSUPIALS. 



575 



they are attached to the nipples at the bottom of the pouch. 

 This large pouch (absent in some opossums and in the 

 Dasyuridm) is supported by two long slender bones attached 

 to the front edge of the pelvis and projecting forward (Fig. 

 495 m and Fig. 497). 



In Thylacinus, the Tasmanian wolf, these bones are car- 

 tilaginous. In the opossum, the kangaroo, and probably 

 most marsupials, the young remains in the pouch attached 

 to the nipple, which fills the mouth. " To this it remains at- 

 tached for a considerable period, the milk being forced down 

 its throat by the contraction of the cremaster muscle. The 

 danger of suffocation is avoided by the elongated and coni- 

 cal form of the upper extremity of the larynx, which is em- 

 braced by the soft palate, as in the Cetacea, and thus respi- 

 ration goes on freely, 

 while the milk passes, 

 on each side of the 

 laryngeal cone, into 

 the oesophagus " 

 (Huxley). In the car- 

 nivorous forms the 

 brain is low in struc- 

 ture, the olfactory 

 lobes being very large, 

 completely exposed, 

 while the cerebral 

 hemispheres are small 

 and quite smooth. 



The dentition of marsupials is characteristic, none having 

 three incisor teeth upon each side, above and below, and 

 none but the wombat (Phascolomys), with an equal num- 

 ber of incisors in each jaw, there being usually more in the 

 upper than in the under jaw. 



The lowest marsupial is the Tasmanian wolf (Thylacinus), 

 which is rather smaller than the wolf. The Tasmanian devil 

 (Dasyurus ur sinus Geoffrey, Fig. 383) is a vicious, trouble- 

 some creature, about the size of a badger. The opossums 

 inhabit North and South America. They have a long tail 

 and a plantigrade step i.e., they walk on the sole of the 

 whole foot. The Virginian opossum (Fig. 407. Didclphys Vir- 



Fi-. 49?'. Opossum (from Tenney's Zoology) and 

 side view of pelvis with the marsupial bone, M. 



