1 6o WHALES 



Figure gi. Right views of the heart of {a) a False Killer and (b) a horse. The right chamber is 

 shown in section to reveal the trabeculae. {Slijper, igjg.) 



shorter. Undoubtedly, similar factors have also affected the shape of the 

 hearts of elephants and sea-cows. Zimmermann's investigations (1930) 

 have moreover shown that there is a certain correlation between the shape 

 of the heart and its strength, so that a racing horse has a more elongated 

 and narrower heart than a carthorse, a wild rabbit a narrower heart than 

 its tame relatives, and so on. The shape of the Cetacean heart would, in 

 that case, indicate that the animal is not equipped with a specially strong 

 organ. Moreover, the ventricles are intersected by a considerable number 

 of muscle bundles or trabeculae (Fig. 91), and according to one of the 

 leading experts on the structure of the mammalian heart, the German 

 anatomist Benninghoff, hearts with highly developed trabeculae generally 

 have a smaller output than others. In this connexion we might also 

 mention that the wall of the right chamber is 2-3 times as thick as that of 

 the left -just as it is in men and other mammals. 



From the entire preceding discussion, we can therefore conclude that 

 no single characteristic of the Cetacean heart makes it more efficient or 

 powerful than that of a terrestrial mammal - if anything, the reverse 

 seems to be the case in the larger species. The reader might wonder why 

 so much time has been spent on showing that there is nothing remarkable 

 about the Cetacean heart. The answer is that this fact is not generally 

 appreciated and, moreover, that without looking at the heart, we would 

 have been unable to go on to a discussion of the rest of the vascular system, 

 and here we shall in fact find the most astonishing peculiarities. 



One of the strangest Cetacean characteristics is undoubtedly the 

 presence of numerous and widespread vascular networks (the so-called 

 retia mirabilia) in the blood system. We may remember from our school 

 days that the arteries, i.e. the vessels that carry blood from the heart to 

 the rest of the body, branch out into ever-finer vessels till finally they 

 become a capillary network. Here, the blood surrenders its oxygen to the 

 tissues and takes up carbon dioxide, then goes on to join up with a system 



