368 
world more 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 aflinity, 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 at 
of nipples in both species, and especially in 
the female of the Oriitherkyuchas pears Hi 
The opinion of Sir Everard Home was soon 
after adopted by Professor Geoffroy St. Hilaire, 
who, inthe Bulletin des Sciences Philomathiques, 
(tom. 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 
Fig. 
MONOTREMATA. 
nerally assented to. The 
erie weit a 0 - one of his vig | 
separat e Myrmecophaga . 
Shaw Soon the true Anteaters san the ic 
term § Echidna,’ and who afterwards con- 
siderable additions to its anatomical history, 
as well as to that of the Ornithorhynchus para- 
doxus, in the Legons d’ Anatomie 
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 Blainville 
more decidedly opposed the opinion of Geof- 
froy, and the latter naturalist in an 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 pg that of Rye Mammals, ex- 
presses his opinion that the mammary organs 
will altimately 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 et bees res details have been given, 
for a knowledge of which, as the Orni- 
thorhynchus, science is chiefly indebted to the 
celebrated Meckel.+ 
168. 
not, however, 
Skeleton of the Echidna Hystriz, (Pander and D' Alton, corrected from Nature. ) 
int, 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 ~ 
OsTEoLocy. 
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 
their constituent pieces continue | dis- 
tinct in the Echidna than in the Ornithorhyn- 
chus; and their relative position, their con- 
< ease Rene de aegeys ee 1797. ; 
t Sce his beautifal Monograph, ‘¢ Ornithorhynchi 
Paradoxi Descriptio Anatomica,” folio, 1826. — 
