180 M. F. Cuvier De I'Histoire 
species would only increase its popularity. This is true of the other 
orders of the animal series. The fossil elk, the great mammoth, the 
extinct rhinoceros, the cave-bear, and many others which might be 
mentioned, are not the least interesting species of their respective gene- 
ra, and are most attractive objects of natural history as beings of a by- 
gone age, not one of which could be distinguished except by a most 
minute comparison with the living species. And surely, therefore, 
in a work like the present, which is altogether of a scientific cast, 
it seems a pity that they should be wholly neglected ; the more so, 
as the science of geology must always turn to the zoologist for all 
the information it desiderates concerning this interesting department 
of its fascinating inquiries. 
We now proceed to lay before our readers whatever appears most 
new and interesting in the work before us. 
The preliminary discourse, extending to fifty pages, is composed 
of a general survey of the order, and dwells more especially on the 
peculiarities of their comparative anatomy. Here our author is mi- 
nute and lucid, describing the internal as well as the external struc- 
ture. One of the most interesting statements relates to a peculia- 
rity of the arterial system, which is connected with the function of 
respiration. It consists in an innumerable congeries, a vast 
plexus of great arteries, which, after respiration, is filled with 
highly purified i)lood, and which is lodged beneath the pleurae, be- 
tween the ribs, and on each side of the spine. The vessels forming 
this plexus rise from the upper intercostals, and they penetrate into 
the vertebral canal, and even into the cranium, by the occipital fora- 
men. The plexus is not formed of ramifications which anastomose with 
each other, for they may in some degree be followed out, and unra- 
velled as if they were only a single vessel twisted a thousand times 
upon itself. In addition to their connection with the intercostals, 
they are also connected with the vertebrals and carotids. They do 
not appear to communicate directly with any vein. The vena azygos 
is not situated anteriorly to the spinal cord, but is replaced by a 
considerable trunk on each side and posteriorly to the cord, which 
receives the intercostal and lumbar veins, and joins the superior ve- 
na cava. It is conceived that this singular structure is connected 
with the occasional long-continued suspension of respiration in the 
Cetacea ; extending to the long period of an hour, and sometimes 
even more. These vessels, it will be seen, become a reservoir of 
highly arterialized blood, which entering gradually into the circula- 
tion will, for a long period, maintain life.* 
* See p. xvii. 90. 
