368 



MONOTREMATA. 



world move strongly towards their remarkable 

 peculiarities and deviations from the ordinary 

 structure of the Mammalia. In these investiga- 

 tions the author having brought to light nume- 

 rous instances of mutual affinity, before con- 

 cealed under very dissimilar exteriors, grouped 

 the two animals together under the same generic 

 appellation, adopting that of Ornithorhynchus, 

 proposed by Blumenbach. He likewise ex- 

 pressed his opinion that they differed consider- 

 ably in their mode of generation from the true 

 Mammalia, on the ground of the peculiarities 

 of the organs themselves, and on the absence 

 of nipples in both species, and especially in 

 the female of the Ornithorhynchus paradoxus. 



The opinion of Sir Everard Home was soon 

 after adopted by Professor Geoffrey St. Hilaire, 

 who, in the Bulletin des Sciences Pliilomathiqv.es, 

 (torn, iii.), constituted a new order for these 

 animals under the term ' Monotremata;' having 

 been led to believe, from an imperfect dissec- 

 tion, that the genital products of both sexes as 

 well as the urine and excrement, were voided 

 by a single common outlet. Concluding, also, 

 by inference that the mammary glands as well 

 as nipples were wanting, and strengthened in 

 his belief of the oviparous nature of the Mono- 

 tremata by some accounts from New South 

 Wales respecting the discovery of the eggs of 

 the Ornithorhynchus,* he subsequently sepa- 

 rated the Monotremata altogether from the 

 Mammalia, and characterized them as a class 

 intermediate to Mammalia, Birds, and Reptiles. 



This mode of viewing the Monotremata was 



not, however, generally assented to. The 

 Baron Cuvier, who in one of his earliest works * 

 had separated the Myrmecophaga aculeata of 

 Shaw from the true Anteaters under the generic 

 term ' Echidna,' and who afterwards made con- 

 siderable additions to its anatomical history, 

 as well as to that of the Ornithorhynchus para- 

 doxus, in the Lemons d'Anatomie Cornparee, 

 whilst he adopted the collective term ' Mono- 

 tremata,' admitted it in the' Regne Animal' as 

 indicative only of a tribe or family in his order 

 Edentata. Spix, Oken, and De Blainville 

 more decidedly opposed the opinion of Geof- 

 froy, and the latter naturalist in an express dis- 

 sertation on the place which the Ornithorhyn- 

 chus and Echidna ought to hold in the animal 

 kingdom, after adducing the numerous instances 

 in which the structure of the Monotremes 

 agrees with that of the true Mammals, ex- 

 presses his opinion that the mammary organs 

 will ultimately be detected, and considers the 

 animals themselves as most closely allied to 

 the Marsupial order. 



The exact position of the Monotremata, their 

 natural affinities, and the value of the group, 

 could, however, be only a matter of speculation 

 before their organization, and especially their 

 cerebral structure, had been thoroughly eluci- 

 dated ; the consideration of these points will 

 therefore be resumed after the requisite anato- 

 mical and physiological details have been given, 

 for a knowledge of which, as regards the Orni- 

 thorhynchus, science is chiefly indebted to the 

 celebrated Meckel.f 



Fig. 168. 



Skeleton of the Echidna Hystrix. (Pander and D' Alton, corrected from Nature.} 



OSTEOLOGY. 



Of the skull. The skull in both genera of 

 Monotremata is long and depressed, but is cha- 

 racterized by a relatively larger cranium in pro- 

 portion to the face than in the Marsupials. The 

 parietes of the expanded cerebral cavity are 

 rounded, and their outer surface is smooth. 

 These characters are most conspicuous in the 

 Echidna, in which the jaws are slender, elon- 

 gated, and gradually diminish forwards to an 



* See Linn. Trans, xiii. p. 621. 



obtuse point, so that the whole skull resembles 

 the half of a pear split lengthwise. The facial 

 angle of the Echidna is 36, that of the Orni- 

 thorhynchus 20, being almost the lowest in the 

 mammiferous class. The cranial bones and 

 their constituent pieces continue longer dis- 

 tinct in the Echidna than in the Ornithorhyn- 

 chus ; and their relative position, their con- 



* Tableau Elementaire de 1'Histoire Nat. 1797. 

 t See his beautiful Monograph, " Ornithorhynchi 

 Paradoxi Dcscriptio Anatomica," folio, 1826. 



