CETACEA. 



577 



gong previously mentioned, which was six feet 

 in length, was three inches and a half long 

 and three inches broad at the base ; the thick- 

 ness of its parietes one line and a half; the 

 carneae columnse are few, and resemble those 

 in man. The tricuspid and mitral valves are 

 of the usual form and structure, but the latter 

 are broader than in man, measuring each one 

 inch three lines across the base. The diameter 

 of the orifice of the pulmonary artery (<) is one 

 inch and a half. The capacity of this vessel 

 is very great, according with the impediments 

 to the transmission of blood through the lungs 

 which must arise from the submarine habits 

 of this animal. In the left auricle (d) the trans- 

 verse pectinated muscular bands are equally 

 if not more developed than in the right. The 

 trace of the foramen ovale is more evident on 

 this side the septum auriculare than in the right 

 auricle ; it appeared as an oblique slit directed 

 upwards, about three lines broad, but was com- 

 pletely closed. 



The parietes of the left ventricle (e) are 

 half an inch in thickness ; there is nothing 

 unusual in the mitral valve or the carneas 

 columnae connected with it ; the inner surface 

 of the ventricle was as usual smooth below the 

 origin of the aorta (f). The breadth of the 

 semilunar valves here was ten lines, the dia- 

 meter of the orifice being one-third less than 

 that of the pulmonary artery. The ductus ar- 

 teriosus was completely obliterated.] 



The heart in the Dolphins and Whales does 

 not appear to have undergone any remarkable 

 modifications; but their arterial system pre- 

 sents a very important one in the infinite 

 circumvolutions of arteries, and the vast ple- 

 xuses of vessels, filled with oxygenated blood, 

 which are found particularly under the pleura 

 and between the ribs, on each side of the spine. 

 [Of this remarkable structure, which was 

 discovered by Hunter, we here subjoin the 

 original description. 



" The general structure of the arteries re- 

 sembles 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 subclavian ar- 

 teries. 



" Animals of this (the Whale) tribe, as has 

 been observed, have a greater proportion of 

 blood than any other known, and there aro 

 many arteries apparently intended as reservoirs, 

 where a larger 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 somewhat similar to 

 that formed by the spermatic artery in the Bull. 

 Those vessels, every 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 other. The medulla spinalis is surrounded 

 with a net-work of arteries in the same man- 

 ner, more especially where it conies out from 

 the brain, where 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 con- 

 tribute to form the anterior part of this plexus. 

 The motion of the blood in such cases must 

 be very slow ; the use of which we do not 

 readily see. 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, 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. 



" In our examination of particular parts, 

 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 astonishment in animals so far exceeding 

 the common bulk as the Whale. Thus the 

 heart and aorta of the Spermaceti Whale ap- 

 peared prodigious, being too large to be con- 

 tained in a wide tub, the aorta measuring a 

 foot in diameter. When we consider these as 

 applied to the circulation, and figure to our- 

 selves that probably ten -or fifteen gallons of 

 blood are thrown out at one stroke, and moved 

 with an immense velocity through a tube of a 

 foot diameter, the whole idea fills the mind 

 with wonder."*] 



It is to be presumed, as has been done, that 

 this singular complication of vessels is caused 

 by the necessity in which the Cetaceans are 

 often placed of suspending their respiration, 

 and consequently the oxygenation of their blood, 

 during a considerable time. These numeerous 

 arteries form, therefore, a reservoir of oxyge- 

 nated blood, which, re-entering the circula- 

 tion, supports life throughout, where venous 

 blood would only produce death. But how 

 this blood is sent to this general system of arte- 

 ries, or what is the peculiar force which acts 

 upon it to this effect, is a point on which we 

 are still reduced to the most vague conjectures, 



* Phil. Trans. 1787. p. 415. It must be supposed 

 that M. Breschet, who has recently written on the 

 arterial plexuses of the Cetacea, could only have 

 known the preceding description by extract or refe- 

 rence, or he would not have stated that the structure 

 in question had been 'observee par J. Hunter, maia 

 indiquees irop sommairement pour pouvoir etre des 

 lors comptes au nombre des faits acquis a la sci- 

 ence,' for we do not find in M. Breschet's paper 

 any essential addition to the original account given 

 by our celebrated anatomist, either with respect to 

 the observation of additional facts, to their clearer 

 description, or to tbe physiological inferences de- 

 duced from them. It is agreeable to find that M. V. 

 Baer, whose observations on the subdivision of 

 the brachial arteries, and on other parts of the 

 vascular system of the Porpesse, are real additions 

 to the anatomical history of the Cetacea, by no 

 means considers it necessary to depreciate the 

 value of the observations of his predecessors in 

 the same field of enquiry. 



