153 



THE OVIPAROUS VERTEBRATES IN GENERAL. 



Although the three classes of Oviparous Vertebrates diiFer very much from each other 

 in their quantum of respiration, and in all that relates to it, viz., the power of move- 

 ment and the energy of the senses, they present several characters in common when 

 opposed to the Mamtnalia, or \^iviparous Vertebrates, [certain of which are partici- 

 pated in by the Ovoviviparous IVlammalla, or the subclass of Marsiipiata and 

 Monotremata] . 



The hemispheres of the brain are much reduced, and [as in the Ovoviviparous 

 Mammaha] 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 

 classes) attain a great development, are hollowed so as to enclose a ventricle, and [as 

 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- 

 tremata'] has not so many small bones, uhich in several are totally wanting ; the 

 cochlea, where it exists, which is only the case in Birds, is much more simjile, &c. 

 Their lower jaw, always composed of many pieces, is attached by a concave facet to a 

 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 

 relative places, and fulfil similar functions ; thus, the frontal is composed of five or six 

 pieces, &c. The orbits are merely separated by an osseous lamina of the sphoenoidal 

 bone, or by a membrane. When these animals possess anterior extremities, in addition 

 to the clavicle, which is often united to its fellow on the opposite side, and is then 

 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 ; 

 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 

 various relations should be adequately appreciated, it would be necessary to enter into 

 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 

 plan on which they are constructed, is greater than that of any of them with the 

 Mammalia. 



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 

 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 e^^, of which the young 

 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 or hrancJdce. 



