ii8 



MOLARS OF EUTHERIA 



cbl 



^TTion 



a.nt.co7n 



of the Marsupials as " singularl)' specialised characters," in no 

 \v;i,y intermediate in character. This ^'iew applies also to the 

 pouch, which, as already stated, distinguishes the adults of that 

 group. But the impossibility of using this last character as 

 one of any importance has been shown by the discovery of 

 rudiments of it in embryos of undoubtedly Eutherian mammals 

 (see p. 18). 



Less stress is laid now upon the existence of four molars in 



the Marsupials as 

 dividing them from 

 the higher mammals 

 than was formerly the 

 case. The total denti- 

 tion of the group is 

 on the whole com- 

 posed of more numer- 

 ous individual teeth 

 than in the typical 

 Eutheria ; but we have 

 Wallaby exceptions like the 

 A^'hales, the Arma- 

 dillo Friodontes, and 

 Manatee ; or 

 better, because free 

 from the suspicion of 

 secondary multiplica- 

 tion, Otocyon and occa- 

 sionally (according to 



rned 



cmajn 



vent.s 



Fig. ."iS. — Sagittal .section of brain of Rod' 



{['rlniijale penicitlata). ant.com, Anterior commis- 

 sure ; cU, cerebellum ; c.mmn, corpus manimillare ; 

 i-.qc, corpora quadrigemina ; crm\ crura cerebri 

 epi, epiphysis, with the posterior commissure ini- . 

 nieiliately behind it ; f.inon. position of foramen of tire 

 Monro ; hiji.com, hippocampal commissure, consist- 

 ing here of two layers continuous behind at the 

 spleneium, somewhat divergent in front where the 

 septum lucidum extends between them ; hijpo, hypo- 

 physis ; met!-, medulla oblongata ; mid.com., middle 

 commissure ; olf, olfactory lobe ; lyrf, optic ohiasnia ; 

 ceiil. .3, third ventricle. (Fi-om Parlicr and Haswell's 

 Zoology.) 



ilr. Thomas) Centetes. 

 In the last two there are at least sometimes four molars. 



On the other liand, a few archaic characters of some import- 

 ance crop up here and there among the ^Marsupials, which are 

 sometimes held to point to a primitive ancestry. It has Ijcen 

 remarked tliat in Marsupials it is the fourth toe which is dominant 

 in size, whereas in Ungulates it is the third. An attempt has 

 been made to explain this on the view (reasonable enough in 

 itself) of a tree-living ancestry for the group. A greater develop- 

 ment of the fourth toe is, however, by no means a necessary 

 character of arboreal creatures ; the Primates themselves are an 

 exception. Nor is this prevalence universal among the Marsupials ; 



