1880.] ARRANGEMENT OP THE MAMMALIA. 653 



7. The malleus is relatively very large ; and the *' processus gra- 

 cilis," which is singularly long and strong, passes between the tym- 

 panic and the periotic bones to the pterygoid, with which it is firmly 

 united. Thus the palato-pterygoid apparatus is directly connected by 

 a "suspensorium " with the periotic, as in the Amphibia and Sau- 

 ropsida. As in these, the representative of the incus is extremely 

 small, and that of the stapes columelUform. 



8. The coracoid is complete, distinct, and articulates with the 

 sternum. 



9. The hip-girdle is provided with large epipubes ; and the iliac 

 axis is inclined at a large angle to the sacral axis. 



10. The corpus callosum is very small. 



11. There appears to be no allantoic placenta, though, from the 

 obvious remains of the ductus arteriosus and of the hypogastric 

 arteries, there can be little doubt that the foetus has a large respira- 

 tory allantois. It is quite possible that, with a large umbilical sac, 

 there may be an imperfect "umbilical" placentation. 



But, while the Ornithorhynchus and the Echidna are thus the 

 representatives of the lowest stage of the evolution of the Mammalia, 

 I conceive it to be equally unquestionable that, as Haeckel has 

 already suggested, they are greatly modified forms of that stage — 

 Echidna, on t!:e wliole, representing a greater, and Ornithorhynchus 

 a less, departure from the general type. The absence of true teeth 

 in both genera is an obvious sign of extreme modification. The long 

 tongue, extraordinary external auditory passages, and relatively large 

 convoluted brnin of Echidna, and the cheek-pouches and horny 

 mouthplates of Ornithorhynchus, are other indications of the same 

 kind. 



Hence the primar}' mammals, which were less modified, and the 

 existence of which is necessarily postulated in the conception of the 

 evolution of the group, cannot, without risk of confusion, be called 

 ISfonotremata or Ornithodelphia, since iu all probability they were 

 as widely different from Ornithorhynchus and Echidna as the Ii:- 

 sectivora are from the Edentata, or the Ungulata from lihytina. 

 Hence it will be convenient to have a distinct name, Prototheria, 

 for the group which includes these, at present, hypothetical embo- 

 diments of that lowest stage of the mammalian type, of which the 

 existing Monotremes are the only known representatives. 



A similar reasoning applies to the Marsupialia. In their essential 

 and fundamental characters they occupy an intermediate position 

 between the Prototheria and the higher mammals. 



1. The mammary glands are provided with teats. 



2. The cloaca is so greatly reduced that it is often said to have 

 disappeared. 



Wirbelkorper/' Zoologischer Auzsiger, 1879, No. 18), while admitting that 

 Echidna has no epipliyses, describes epiphyses of an incomplete character be- 

 tween the posterior twelve caudal vertebrw of Ornithorhynrhus. So far as I am 

 aware, the memoir, of which Dr. Albreeht has given a preliminary notice. 

 has not yet been published ; I content myself therefore with remarking that 

 niy own recent observations are in harmony with Dr. Albrecht's statement, 



