Cetacea.- 



-MAMMALIA.- 



-Cetacea. 



195 



themselves in various directions. Often liave we gazed 

 upon tliis rete mirabile, as it is called, with astonishment ; 

 and although it has been figured by several autliors, 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 (fig. 77). This 

 structure was iirst acciu'ately described and explained 

 by tiie celebrated John Hunter, who observes that 

 " the intercostal arteries divide into a vast number of 

 branches, which nm in a sei'pentine course betweert tiie 

 pleura, ribs, and their muscles, making a thick substance, 

 somewhat similar to the spermatic artery in the bull. 

 These vessels everj'where lining the sides of the thorax, 

 pass in between the ribs near their articulation, and also 

 behind the ligamentous attachment of the ribs, and 

 anastomose with each otlier. The medulla spinalis is 

 surrounded with a network of arteries in the same man- 



Intercostal arterial plexus or ' rete mirabile of the Porpoise 

 (PhocEena communisj. 



ner, more especially where it comes out irom the brain, 

 while a thick substance is formed by their ramifica- 

 tions and convolutions; and these vessels most probably 

 anastomose with those of the thorax. The subclavian 

 artery in the Piked whale, before it passes over the 

 first rib, sends down into the chest arteries wliich assist 

 in forming the plexus on the inside of the ribs. I am 

 not cei-tain but the internal mammary arteries contri- 

 bute to form the anterior part of this plexus. The 

 motion of the blood in such cases must be very slow." 

 He also adds: — " The descending aorta sends off the 

 intercostals which are very large, and gives branches to 

 this plexus; and when it has reached the abdomen, it 

 sends off, as in the quadruped, tlie different branches to 



the \'iscera and the lumbar arteries, which are likewise 

 very large, for the supply of that vast mass of muscles 

 which moves the tail." As regards the function ot 

 this vascular apparatus, it is evidently connected with 

 the power which whales have of remaining under water 

 for a long period without coming to the surface, some 

 species having been known, when hai-pooned, to be 

 submerged for an hour and a half at a time. Co-ordi- 

 nating with the habits of these animals, we 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 homy substance, 

 or whalebone, as it is commonly termed, are essentially 

 developments of the cuticular layer of the skin. As 

 their special function is to entangle within their layers 

 various medusae and small molluscous animals, the 

 lower or depending end of each plate is split up into a 

 multitude of fibres, which, acting like a sieve, render 

 their chance of escape the more hopeless ; upwards of 

 three hundred such baleen plates occurring on either 

 side of the upper jaw m the common mysticete. The 

 throat of the whale 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 swallowed. The whale having come 

 upon a swarm of molluscs, or pteropods such as the 

 little Clio borealis, multitudes are immediately en- 

 tangled in the baleen; and when a sufficient number 

 have accumidated, the enormous tongue is raised for- 

 wards and \ipwards, and thus by one fell swoop of this 

 organ, the unsuspecting mass are hurled backwards 

 towards the gullet, the water strained from them at the 

 same time escaping upwards through tlie blow-hole in 

 the foim of a conspicuous Jei cTeau. Although the full- 

 grown mysticetes are supplied witii these homy plates 

 for the prehension of their peculiar food, it is not tme 

 to say that they have no teeth at any stage of their 

 existence; for, in tiie foetal condition, as the indepen- 

 dent researches of Geoffroy St. Hilaire, Eschricht, and 

 Goodsir have shown, and as we have had an opportunity 

 of witnessing, the lower jaw is fiunished with numerous 

 distinct dental sacs, each of which contains the rudi- 

 ments of a separate tooth. Here again, tlierefore, we 

 observe a remarkable conformity to type, in the rudi- 

 mental development of organs, which, as they can never 

 be required in after life, are consequently never brought 

 to a state of perfection ! Consistently with other 

 peculiarities of their organisation, the stomachs of the 

 Cetacea are all more or less comphcated. Differences 

 of opinion exist as to tiie degree of complexity in 

 various species, but on the whole they do not depart 

 materially from that which has often been described, 

 and which we have ourselves observed to obtain in the 

 common porpoise. In this species — as also in the 

 white whale, from which the annexed cut (fig. 78) is 

 taken — the organ consists of tour distinct ca^^ties ; but 

 in respect of relative bulk and function, it cannot in 

 any measure be said to correspond mth the multiple 

 stomach of the rmninating quadrupeds. These com- 

 partments commimicate with each other continuously, 

 and are not supplied with special reservoirs, reticula- 

 tions, or laminaj, such as are observable m the mminant 



