542 EDENTATA. 



MONODELPHIA. 



(Sometimes called Eiitheria.) 

 This group includes the remaining orders of the Mammalia. 

 The urinogenital organs almost always open independently of 

 the rectum, and the vagina is single, though occasionally it is 

 partly divided into two by a median septum. There is no 

 marsupial pouch nor epipubic bones. The embryo is always 

 provided witli an allantoic placenta and born at an advanced 

 stage of development. The corpus callosum of the brain is 

 well-developed. The testes usually pass into a scrotal sac, 

 which is always placed at the sides of or behind the penis. 



Order 3. EDENTATA * (BRUTA). 



Mammals ivith incomplete dentition, usually with numerous 

 grinders tviihout roots, and laith scratching or curved claws on the 

 extremities. Teeth are always absent from the anterior fart of 

 the mouth, and they are without enamel. 



This order, which includes but few genera (sloths, anteaters, 

 armadillos), is characterised by the relatively low grade of 

 development of all the organs, and especially by tlie incom- 

 pleteness of the dentition, teeth being in exceptional cases 

 absent altogether. Except in the case of a single dasypod, 

 incisors are always absent. When canines are present they are 

 small, blunt and conical. All the teeth are devoid of enamel, 

 consisting of soft dentine covered externally by hard dentine 

 and sometimes cement, and they grow from persistent pulps 

 (rootless). With the exception of some armadillos {Tatusia, 

 etc.) and Orycteropus, milk teeth are not formed, and there is no 

 replacement (monophyodont). The ischium is almost always 

 united to the sacrum. The brain is variable ; the cerebrum 

 may be smooth and the corpus callosum small, or it may be 

 convoluted and possess a large corpus callosum. The repro- 

 ductive organs are also variable. The vestibule (urinogenital 

 canal) of the female is long, and the testes almost always remain 

 in the body. There are two superior venae-cavae, and retia 

 rairabilia are often present in the extremities. 



* W. v. Rapp, Anatomische Unters. ilber die Edentatcn, Tubingen, 1852. 

 n. Ameghino, Sur les Edentcs Fossiles de 1' Argentine, Revista del Jard. 

 Zool. de Buenos-Aires, iii, 1S95, p. 11.1. R. Lydekker, Ann. Miis. La 

 Plata, Palaeont. Argentina, iii, 189.3. For Ribliography, see Flower 

 and Lydekker' s Mammals Living and E.xiinct, 1891. 



