173 ESCHRICHT ON THE 



circumstance which often produces in them a peculiar morbid condition, excited by friction. 

 For the conical teeth in the upper and lower jaws of the killers are very regularly fitted in between 

 each other, so that in general they are not easily exposed to any friction at the points, at least not 

 at the beginning. But having such a considerable breadth, and being placed close to one 

 another, the inevitable consequence is that they become worn on the lateral surfaces. Even in 

 very young teeth, we find an elongated concave friction mark on one of the sides ; in the 

 upper jaw most commonly on the anterior and external sides of the teeth, but on the lower jaw in 

 the posterior and internal sides. The more excavated this worn surface becomes, the deeper of 

 course the teeth of the two jaws will be wedged in between each other. Soon, most of the 

 teeth are worn by both of the opposite ones. The worn surfaces meet each other at the point, 

 which is completely worn off, and the originally conical teeth, with their decidedly pointed, 

 if not very sharp, ends, are now changed into real flat and obtuse teeth. As in all other real, 

 that is to say, enamelled crowns of teeth, the portion once worn ofi" is not compensated for 

 by a growing out of the root of the tooth, and in old killers all the crowns of the teeth 

 may be found worn down to the very gums. This was the case with the specimen of Mr. 

 Benzon. This wearing ofi" does not generally take place until the formation of the dentine 

 in the crowns has been completed, or until the crowns of the teeth are perfectly ossified. But 

 not unfrequently it happens otherwise, and then the wear penetrates both the enamel and the 

 still thin layer of the dentine, so that the pulp is exposed and dies away, and the formation 

 of the dentine is not only stopped in the crown, but also in the root which is never closed, 

 and the whole tooth remains hollow from the worn surface down to the point of the root. 

 Nevertheless, such decayed teeth do not fall out. 



According to what we have stated above, the teeth of the Orcas are of a quite different kind 

 from those of the cachalots, which have only spurious or not enamelled dental crowns, like those 

 of the belugas, except in their earliest age. They belong, on the contrary, to the canine 

 kind as those of the true dolphins, the common porpoises and the ca'ing-whales, as far as 

 the teeth of all these animals have also real or enamelled crowns. By its form, and more 

 especially by its superior thickness, an Orca tooth is, nevertheless, even more easily distinguishable 

 from any of the teeth of the latter Cetaceans, than by its structure from those of the cachalots. 



It has already been remarked in the description of the exterior of the rapacious whales, that 

 they may as easily be distinguished from all other toothed Cetaceans by the form and size of 

 \kt pectoral fins, as by the height and shape of the dorsal fin. The same remark may be applied 

 to each of the bones of the pectoral fins. As to the scapula it need only be said, that it is 

 easily distinguished from that of the ca'ing-whale and all other large toothed whales, by its 

 strong marks and ridges for the insertion of the muscles, and especially by its having its spine 

 with the acromion placed sufficiently far behind the anterior edge as not to hide the part of the 

 external surface [Fossa supraspinata) which is placed before it, v^hereas this part of the scapula 

 of other great toothed Cetaceans is not easily visible, except from the anterior edge ; evidently 

 a proof of the greater development of the muscles, and especially of the muscle [M. supraspinatus) 

 attached to this hollow. 



As an illustration of the peculiar structure of the arm and the manus of the killers, we have 

 inserted a woodcut representing at a scale four times reduced, the left pectoral fin of the thirteen 

 feet long individual of Mr. Thomsen (captured at Aarhuus, 1855), as it appeared six days after 

 the preparation of the skeleton. The whole length of the arm was 22^". Of this length the 



