Cetacea.- 



-MAMiMALIA.- 



-Cetacea. 



193 



Two or three more species have been described. Of 

 these may be mentioned, Smith's Hyrax {Hyrax 

 arhoreus) from South Africa; this form possessing 

 arboreal habits, and being distinguished by its longer 

 fur, which also displays a white spot on tlie back. 

 Anotlier species, capable of climbing trees and feeding 

 on their fruits, is the Hyrax Sylvcstris of Temminck. 



This form inhabits New Guinea and other parts on tlie 

 west coast of Africa, and it is remarkable as possessing 

 only twenty -four grinding teeth ; that is, three pre- 

 molars and three true molars on each side of either 

 jaw, the orbital ring bemg at the same time more 

 complete than obtains- in any other member of the 

 family. 



Order XII.— CETACEA. 



Although scientific naturalists have imiformly insisted 

 on the maramiferous character of the cetacea — at least 

 since the days of Cuvier, and also, m some degi-ee, 

 from the time of Linnaeus — the majority of 

 people stiD class them with fishes; but the only 

 grounds on which these animals can with any 

 propriety be said to resemble the finny tribe, 

 are those which refer to their form and the 

 conversion of the anterior limbs into finlike 

 paddles. Even heie, however, a close inspec- 

 tion of tlie leathery hide, of the modified hmbs, 

 and of the horizontal tail, is sufficient to indicate 

 a wide departure from the fishes properly so 

 called, in which the tail is vertical, the fins 

 composed of numerous rays, and the integu- 

 ments more or less converted into separable 

 scales; and what is still more distinctive, we 

 also find conspicuous indications of the repro- 

 ductive organs externally, as well as mammary 

 glands in the female. Anatomical investi- 

 gation has likewise shown that these gigantic denizens 

 of the deep breathe by means of lungs, and tliat 

 they have a pulmonic and systemic circulation, as 

 obtains in other mammals. Taking tlie skeleton of 

 the common Greenland whale — Plate 32, fig. 90 — as a 

 t^fpe of zoophagous cetacea, it is extremely interesting 

 to observe how its several osseous elements have 

 become modified in form, and altered in bulk, in order 

 to meet tlie exigencies of a creature destined to live in a 

 medium so different from that generally enjoyed by the 

 mass of mammalian vertebrates. Commencing with 

 the head, the first thing that strikes us is the remark- 

 able extension of the bones of the face, the inter-max- 

 illary and superior maxillary bones arching forwards to 

 form a kuid of rostrum, whilst the lateral divisions of 

 the lower jaw converge towards tlie tip of the snout, 

 forming a curve on either side scarcely less conspicuous. 

 Tlie cranial bones are not less altered ; the nasals are 

 short, the temporals square-shaped, the frontals remark- 

 ably narrowed and directed obliquely outwards and 

 backwards, the vertex of the skuU being almost entirely 

 occupied by the upper flattened portion of the occipital 

 bone. All these characters are well displayed in the 

 accompanying woodcut (fig. 76). If our attention be 

 next du'ected to the vertebral column, we find on the 

 one hand an almost complete abrogation of the cervical 

 region, and a striking augmentation of the caudal ele- 

 ments on the other; taken as a whole, however, the 

 bone-chain is massive and well developed. The most 

 interesting feature in connection with this part of the 

 _Yui.._X 



skeleton has reference to the vertebrae of the neck, 

 which in all cases maintain tlieir tjijical number, 

 although, in tlie true whales, they are completely ossified 



Fig. 76. 



SkuU of the Greenland Whale (Bal*ua Mysticetus), 

 seen from above. 



together so as to form a single mass, more or Jess 

 fissured by deep clefts, which serve to indicate the 

 original existence of seven distinct vertebrae in the 

 embryonic condition. But this is only true of the 

 whalebone whales, for in other members of the order 

 the several segments are more or less free ; there being 

 six anchylosed together in the spermaceti, and two 

 only in the piked-whales, the dolphins, and the por- 

 poises ; in the latter the first and second vertebrifi are 

 conjomed ; but in the Balanopterae the union takes 

 place between the second and third cervical segments. 

 In the herbivorous cetacea all the bones are perma- 

 nently free, and this is also the case in the sou-sou or 

 dolphin of the Ganges. In regard to the dorsal and 

 lumbar vertobrEe, all that we need remark is, that both 

 series vary in number, in different genera, while their 

 spinous and transverse processes become more and 

 more conspicuous as they approach the caudal series. 

 One, two, or three vertebrae have been assigned to the 

 sacral or pelvic region, but tliese do not differ in 

 structure from the previous group; and but for the 

 existence of rudimentary pelvic bones, it would be 

 scarcely fair to say that any should be classed in this 

 category. The vertebrae of the tail are exti-emely 

 numerous, upwards of thirty being present in the 

 Rorqual ; sti-ucturally they vary quantitively and mor- 

 phologically, gradually diminishing m bulk and com- 

 plexity of outline from before backwards, until we 

 ultimately find them reduced to a simple compressed 

 nodule at die free extremity of tlie organ. Of the rudi- 



2B 



