153 
j 
i THE OVIPAROUS VERTEBRATES IN GENERAL. 
jl Although the three classes of Oviparous Vertebrates differ very much from each other 
in their quantum of respiration, and in all that relates to it, viz., the power of move- 
I ment and the energy of the senses, they present several characters in common when 
! opposed to the Mammalia, or Viviparous Vertebrates, [certain of which are partici- 
i pated in by the Ovoviviparous Mammalia, or the subclass of Marsupiata and 
I Monotremata '] . 
I' The hemispheres of the brain are much reduced, and [as in the Ovoviviparous 
j Mammalia] are not united by a corpus callosum ; the crura of the cerebellum do not 
|! form that protuberance called the pons Varolii; the nates (at least in two of these 
I classes) attain a great development, are hollowed so as to enclose a ventricle, and [as 
j in the Ovoviviparous Mammalia] are not covered by the hemispheres, but are visible 
below or on the sides of the cerebrum, [which last statement does not apply to the 
|| Ovoviviparous Mammalia] ; their nostrils are less complex ; the ear [as in the Mono- 
|i trematd\ has not so many small bones, which in several are totally wanting; the 
j cochlea, where it exists, which is only the case in Birds, is much more simple, &c. 
I Their lower jaw, always composed of many pieces, is attached by a concave facet to a 
I salient process, which belongs to the temporal bone, but is separated from its petrous 
! portion ; the bones of the cranium are more subdivided, though they occupy the same 
I relative places, and fulfil similar functions ; thus, the frontal is composed of five or six 
jl pieces, &c. The orbits are merely separated by an osseous lamina of the sphoenoidal 
i bone, or by a membrane. When these animals possess anterior extremities, in addition 
I to the clavicle, which is often united to its fellow on the opposite side, and is then 
j termed fourchette, the scapular also rests upon the sternum, by means of a very large 
and prolonged coracoid apophysis. The larynx is more simple, and has no epiglottis ; 
I the lungs are not separated from the abdomen by a perfect diaphragm, [except in the 
|| single instance of that extraordinary bird, the Apteryx'], ^c. But in order that these 
I various relations should be adequately appreciated, it would be necessary to enter into 
i anatomical details, which do not belong to this first part of our work. It is sufficient 
! to have here pointed out the mutual analogy of the Ovipara, which, in reference to the 
I plan on which they are constructed, is greater than that of any of them with the 
j Mammalia. 
j Oviparous generation consists, essentially, in this ; that the young animal is not 
attached by a placenta to the parietes of the uterus, or of the oviduct, but remains 
|| separate from it by its most external envelope, [all which applies to the Ovoviviparous 
j Mammalia] . Its aliment is prepared beforehand, and enclosed in a sac attached to its 
intestinal canal ; being what is termed the vitellus, or yolk of egg, of which the young 
I animal is a sort of appendage, at first imperceptible, which is nourished and augmented 
by absorbing the fluid of the yolk. Such of the Ovipara as breathe by lungs, have the 
egg furnished with a highly vascular membrane, which appears to serve for respiration ; 
it is connected with the bladder, and represents the allantoid of Mammalia. This 
membrane is neither found in Fishes, nor the Batrachians ; which latter, when young, 
respire in the manner of Fishes, by gills ox branchics. 
1 
