MONOTREMATA. 
21 
Zoological Society 1 , Professor Owen has thrown much light 
on this interesting subject : —the discovery of the mammary 
glands, by Meckel, has been confirmed, and a great amount 
of evidence is brought forward tending to prove that the 
Monotrematn arc allied to the Marrtujnata, and art? essen¬ 
tially ovo-viviparous mammals,—that they bring forth living 
young, — and that these are suckled by the parent. 
Prof. Owen and some other authors agree in regarding the 
Monotrcmata as forming a distinct order of the class Mam¬ 
malia and subclass Marsupiata,—an order which presents the 
lowest grade of organization among mammals, and which 
approaches most nearly to the oviparous classes of birds and 
reptiles. 
The most essential characters of die group are strictly ana¬ 
tomical, and we must content ourselves here with a mere 
notice of some among the more striking points. The Mono¬ 
trematn, observes Prof. Owen, are allied to the Marsupiata 
by the absence of the corpus callosum , and by the presence 
of die marsupial bones, but difier in the absence of the abdo¬ 
minal pouch, and in not possessing teeth ; in the simplicity 
of the bigeminal bodies, and in some remarkable modifications 
of the skeleton and generative organs. 
The corpus callosum , it may he necessary to explain, is a 
portion of die brain which forms a kind of band connecting 
the two hemispheres of die brain, and that its presence was 
regarded as peculiarly characteristic of the mammalian order 
(it being absent in birds and reptiles, &c.), until Prof. Owen 
discovered that this band was wanting in the Marsupiata. 
Tho bigeminal bodies also form part of the brain, and come 
into view immediately upon separadng the hinder part of tlie 
great hemispheres. In ordinary quadrupeds, the mass, here 
called bigeminal bodies, is divided by a transverse and a 
1 On the Young of Ornithorhynchus Paradoxu -r, Trans. Zool. Soc. vol. i. 
p. 221. 
