-MAMMALIA.- 
-Cetacea. 
195 
Cetacea. 
themselves in various directions. Often have we gazed 
upon this rete mirabile, as it is called, with astonishment; 
and although it has been iigured by several authors, and 
especially by Breschet, from whose memoir the an- 
nexed cut is given, none of these representations 
fully portray the singularly complicated appearance 
produced by these vascular tortuosities (tig. 77). This 
structure Avas first accurately described and explained 
by the celebrated John Hunter, Avho observes that 
“ the intercostal arteries divide into a' vast number of 
branches, Avhich run in a serpentine course betAveen the 
pleura, ribs, and theirmuscles, making a thick substance, 
someAvhat similar to the spermatic artery in the bull. 
Tb.ese A'essels everyAvhere lining the sides of the thorax, 
pass in betAveen the ribs near their articulation, and also 
behind the ligamentous attachment of the ribs, and 
anastomose Avith each other. The medulla spinalis is 
surrounded Avlth a network of arteries in the same man- 
77 . 
Intercostal arterial plexus or ‘ rete mirabile of the Porpoise 
(Phocama communis). 
ner, more especially Avhere it comes out from the brain, 
Avhile a thick substance is formed by their ramifica- 
tions and convolutions; and these vessels most probably 
anastomose Avith those of the thorax. The subclavian 
arteiy in the Piked Avhale, before it passes o\mr the 
first rib, sends doAvn into the chest arteries Avliich assist 
in forming the plexus on the inside of the ribs. I am 
not certain but the internal mammary arteries contri- 
bute to form the anterior part of this plexus. Tlie 
motion of the blood in such cases must be A'cry sIoav.” 
He also adds: — “ The descending aorta sends off the 
intercostals Avhich are very large, and gives branches to 
this plexus; and Avhen it has reached the abdomen, it 
sends off, as in the quadruped, the ditferent branches to 
the viscera and the lumbar arteries, Avhich are likewise 
A'ery large, for the supply of that vast mass of muscles 
Avhich moves the tail.” As regards the function ot 
this vascular apparatus, it is evidently connected Avith 
the power Avhich Avhales have of remaining under Avater 
for a long period without coming to the surface, some 
species having been knoAvn, Avhen harpooned, to be 
submerged for an hour and a half at a time. Co-ordi- 
nating Avith the habits of these animals, Ave also find 
peculiar modifications of the digestive organs. In the 
true whales, numerous plates of baleen are developed 
from the upper jaw. These laminae of horny substance, 
or Avhalebone, as it is commoidy termed, are essentially 
deA’elopments of the cuticular layer of the skin. As 
their special function is to entangle Avithin their layers 
various meduste and small molluscous animals, the 
lower or depending end of each plate is split up into a 
multitude of fibres, Avhich, acting like a sicA'e, render 
their chance of escape the more hopeless; upAvards of 
three hundred such baleen plates occurring on either 
side of the upper JaAV in the common mysticete. The 
throat of the Avhale is comparatively small, and conse- 
quently adapted only for the passage of minute animals; 
in order, therefore, to obtain sufficient food to nourish 
its bulky frame, it is evident that millions of creatures 
must be hourly sAvalloAvcd. The Avhale having come 
upon a SAvarm of molluscs, or pteropods such as the 
little Clio borealis, multitudes are immediately en- 
tangled in the baleen; and Avhen a sufficient number 
haA'e accumulated, the enormous tongue is raised for- 
Avards and npAvards, and thus by one fell SAvoop of this 
organ, the unsuspecting mass are hurled backAvards 
toAvards the gullet, tlie Avater strained from them at the 
same time escaping upAvards through the bloAV-hole in 
the form of a conspicuous yet d'cau. Although the full- 
groAvn mysticetes are supplied Avith these horny plates 
for the prehension of their peculiar food, it is not true 
to say that they have no teeth at any stage of their 
existence; for, in the foetal condition, as the indepen- 
dent researches of Geofi’roy St. Hilaire, Eschricht, and 
Goodsirhave shoAAm, and as Ave liaA’e had an opportunity 
of Avitnessing, the lower JaAv is furnished Avith numerous 
distinct dental sacs, each of Avhich contains the rudi- 
ments of a separate tooth. Here again, therefore, Ave 
observe a remarkable conformity to type, in the rudi- 
mental development of organs, Avhich, as they can never 
be required in after life, are consequently never brought 
to a state of perfection ! Consistently Avith other 
peculiarities of their organisation, the stomachs of the 
Cetacea are all more or less complicated. Differences 
of opinion exist as to the degree of complexity in 
A'arious species, but on the Avhole they do not depart 
materially from that AAdiich has often been described, 
and Avhich Ave have ourselves observed to obtain in the 
common porpoise. In this species — as also in the 
Avhite AAdiale, from Avhich the annexed cut (fig. 78) is 
taken — the organ consists ©f lour distinct cavities; but 
in respect of relatiAm bulk and function, it cannot in 
any measure be said to correspond Avith the multiple 
stomach of the ruminating quadrupeds. These com- 
partments communicate Avith each other continuously, 
and are not supplied Avith special reservoirs, reticula- 
tions, or laminae, such as are observable in the ruminant 
