The following is John Hunter's description of the heart of the Whale :— " The heart is inclosed in its pericardium, which is attached by a broad surface to the diaphragm, as in the human body. It is com posed of four cavities—two auricles and two ventricles : it is moro flat than in the quadruped, and adapted to the shape of the chest. The auricles have more fasciculi, and then pass more across the cavity from side to side, than in many other animals ; besides being very muscular they are very elastic, for being stretched they contract again very considerably. There is nothing uncommon or particular in the structure of the ventricles, in the valves of the ventricles, or in that of the arteries. The general structure of the arteries resembles that of other animals ; and where parts are nearly similar, the distribution is likewise similar. The aorta forms its usual curve, and sends off the carotid and subclatrian arteries. The veins, I believe, have nothing particular in their structure, excepting in parts requiring a peculiarity, as in the folds of the skin on the breast in the Piked Whale, where their elasticity was to be increased." This assertion respecting the veins is not stated very positively, and we shall presently see that there is a peculiarity in their structure.
The same great physiologist well observes, that in our examination of particular parte, the size of which is generally regulated by that of the whole animal, if we have only been accustomed to see them in those which are small or middle sized, we behold them with astonish ment in animals so far exceeding the common bulk as the Whale. says Hunter, "the heart and aorta of the Spermaceti Whale prodigious, being too large to be contained in a wide tub, the aorta measuring a foot in diameter. When we consider these as applied to the circulation, and figure to ourselves that probably 10 or 15 gallons of blood are thrown out at one stroke, rnd moved with an immense velocity through a tube of a foot diameter, the whole idea fills the mind with wonder." But the most remarkable modification of the arterial system in the Whales remains to be noticed. This consists in an almost infinite circumvolution of arteries, forming a plexus of vessels filled with oxygenated blood, situated under the pleura and between the ribs, on each side of the spine. This intercostal plexus, or rete mirabile, is the apparatus which enables the whale to remain under water for more than an hour.
3L Breschet read a paper to the French Academy of Sciences in 1834, which bears the following title: Histoire Anatomique et Phy siologique d'un Organe de Nature vasculaire decouvert dans les Cetaces, etc.' M. Breschct has however no claims to the discovery of this organ. It was indicated and described long ago by Tyson in his ' Anatomy of a Porpesse,' but he was not aware of the use of it, and considered it as a glandulous body. Hunter was the first who deter mined its exact nature, and showed that it was a reservoir of arterial or aerated blood.
After noticing the general structure of the arteries as above men tioned, and stating that the aorta forms its usual curve, sending off the carotid and subclavian arteries, Hunter proceeds as follows :— " Animals of this tribe, as has been observed, have a greater pro portion of blood than any other known, and there are many arteries apparently intended as reservoirs, where a large quantity of arterial blood seemed to be required in a part, and vascularity could not be the only object. Thus we find that the intercostal arteries divide into a vast number of branches, which run in a serpentine course between the pleura, ribs, and their muscles, making a thick substance, some what similar to the spermatic artery in the Bull. These vessels, everywhere 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 other. The medulla spinalia
is surrounded with a net-work of arteries in the same manner, more especially where it comes out from the brain, whore a thick substance is formed by their ramifications 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 which assist in forming the plexus on the inside of the ribs. I am not certain but the internal mammary arteries contribute to form the anterior part of this plexus. The motion or the blood in such cases must be very slow ; the use of which we do not readily see. The descending aorta sends off the intercostels, which are very large, and gives branches to this plexus; and when it has reached the abdomen it sends off as in the quadruped, the different branches to the viscera and the lumbar arteries, which are likewise very large, for the supply of that vast mass of muscles which moves the tail." With regard to the veins, Professor Owen points out that they are remarkable not only for their great capacity, which Hunter noticed, but also for their number and the immense plexuses which they form in different parts of the body, and above all for the almost total absence of valves. Tyson, he observes, has given a figure of the extensive venous plexus situated on the membrane investing the 1130 RA muscles, and these have recently occupied the attention of Breschet and Von Baer. The inferior and superior venn cave are not brought into communication by the vena azygos, as in other Mammalia ; such veins in the usual situation in the chest would have been subject to compression between the arterial plexuses and the lungs. The ven.13 azygos are therefore represented by two venous trunks situated in the interior of the vertebral canal, where they receive the intercostal and lumbar veins, and finally communicate with the superior cave by means of a short single largo trunk, which penetrates the parietes of the posterior and right side of the chest. Professor Owen concludes this interesting note to Hunter's 'Aninial Economy' by clearing up the difficulty, which must have occurred to most., of accounting for the fact of so enormous an animal as the great whale being killed by such puny instruments as the harpoon and lance. " The non-valvular structure of the veins in the Cetacea," says the Professor, "and the pressure of the sea-water at the depths to which they retreat when harpooned, explain the profuse and deadly hemorrhage which follows a wound that in other Namnudia would be by no means fatal." Respiratory Systcm.—Phytophagous Cetaceans.—Professor Owen states that the peculiar form, structure, and position of the lungs have been so accurately described and figured by Raffles, Home, and Ituppell, that he has only to observe the close agreement with those accounts which the structure of the parts presented in the three Dugongs dissected by him. Daubenten and Humboldt, he remarks, describe and figure a precisely similar condition of the respiratory apparatus in the Manatee. Steller, ho adds, describes the same extension cf the lungs in the Rytiaa, and compares it with the lungs in the Bird, but without their fixation in the parietes of the chest, so characteristic of that class. Professor Owen is of opinion that the Chelonian reptiles perhaps offer a closer resemblance to the lierbivo roue Ctlacea in this respect ; and he notices it as worthy of remark, that the air-cells of the lunge are larger in the Dugong than in any other manmials. In the Carnivorous Cetacen, the air-cells, ho observes, are remarkably minute, and the lungs more compactly shaped and lodged in a shorter thorax.