194 



CETACEA.- 



-MAMMALIA. CETACEA. 



mentary character of the pelvic bones we have already 

 spoken, their attenuated form bearing no resemblance 

 to the ilia of those quadrupeds in which the posterior 

 limbs are present. The ribs are chiefly noticeable in 

 respect of their mode of articulation to the dorsal ver- 

 tebrae and the great degree of curvature, which is 

 necessary to make room for the bulky thoracic viscera; 

 a few of the anterior ribs are articulated by their 

 heads to the bodies of the vertebrae and by a tubercle 

 to the transverse processes, but the remainder have 

 only a single mode of connection and have no true 

 articular facets at their attached ends. The paddles or 

 anterior extremities are worthy of particular considera- 

 tion. In them, as has been already hinted, are to be 

 found evidences of conformity to type, having a signi- 

 ficance not less forcible than that enunciated when 

 treating of the bones of the neck. Viewing the limb 

 from without, there is nothing to indicate the parts 

 severally denominated arm, fore-arm, and shoulders; 

 but upon dissection we find all the osseous elements 

 ordinarily entering into the constitution of these seg- 

 ments fully represented and easily recognized. With 

 the exception of the humero-scapulur articulation, all 

 the bones are firmly invested and packed together by 

 fibrous tissue, so as to prevent motion upon one 

 another; and what is more noticeable, is, that they 

 have all become shortened lengthwise, whilst their 

 breadth has somewhat increased, as it were, by com- 

 pression within the tightly investing teguments. In 

 some species, as in the common mysticete, the digital 

 phalanges are more numerous than usually obtains in 

 the feet of pentadactyle quadrupeds. If we turn our 

 attention to the skeleton of any of the herbivorous 

 cetacea such, for example, as that of the Dugong, Plate 

 34, fig. 109 not only do we observe a less consider- 

 able departure from the ordinary mammalian type, as 

 instanced by a comparison of the bones of the hand, 

 arm, fore-arm, and shoulder; but in contemplating the 

 structure of the head and neck, it is evident that we 

 have moved a step higher in the scale of organization. 

 The seven cervical vertebrae are distinct, though still 

 remarkably compressed from before backwards, and 

 the skull, whilst visibly contracted in the same direc- 

 tion, presents, nevertheless, several peculiarities suffi- 

 ciently cogent to demand special notice ; these will be 

 immediately considered when describing the general 

 characteristics of the Manatidae. Meanwhile we pass 

 on to notice very briefly, some of the more striking 

 modifications of the viscera, as well as other internal 

 and external arrangements equally suggestive. And, 

 firstly, as respects the organs of respiration which are 

 chiefly to be noted on account of their singular com- 

 munication with the air by means of two nostrils 

 situated at the top of the head in the true whales, and 

 by a single opening similarly placed in the dolphins; 

 in the herbivorous species these passages terminate in 

 front of the muzzle, as in mammalia generally. Hav- 

 ing, on several occasions, dissected the common porpoise 

 with very great care, we are in a position to testify to 

 the accuracy of Baron Cuvier's account of the singular 

 manner in which the windpipe terminates, especially 

 within a vertical extension of the pharynx, which is 

 commonly designated the spouting apparatus, the exter- 



nal openings above being vulgarly called the blow-holes. 

 "If we trace the oesophagus upwards," says Cuvier, 

 " we find that when it arrives opposite the pharynx, it 

 appears to divide into two passages, of which one is 

 continued onwards to the mouth, while the other 

 mounts to the nose; this latter passage being sur- 

 rounded with mucous glands and fleshy muscular 

 bundles. Some of these are longitudinal, arising from 

 the circumference of the posterior orifice of the bony 

 nostrils, and descending along that canal to the pharynx, 

 and its lateral path. The others are annular and 

 appear to be a continuation of the proper muscle of the 

 pharynx, and as the larynx rises into this passage in 

 the form of an obelisk or pyramid, these annular fibres 

 have the power of grasping it by their contractions. 

 Mucous follicles which empty their secretion by conspi- 

 cuous excretive orifices are abundant at this part. The 

 lining membrane of the nasal passage having reached 

 the vomer, assumes a peculiar texture; becoming thin, 

 smooth, very dry, of a black colour, and apparently 

 destitute of nerves and vessels. The two osseous 

 nasal canals are closed at the superior or external ori- 

 fice by a fleshy valve in the form of two semicircles, 

 attached to the anterior margin of that opening, which 

 it closes by means of a very strong muscle lodged above 

 the intermaxillary bones. In order to open it some foreign 

 body must press against it from below. When this 

 valve is closed, it cuts off all communication between 

 the nasal passages and the cavities above them. These 

 cavities consist of two large membranous pouches 

 formed by a dark-coloured mucous skin, which is much 

 wrinkled when they are empty; but assuming, when 

 distended, an oval figure, which in the porpoise equals 

 the size of a common wine-glass. These two pouches 

 are lodged beneath the integuments, in front of the 

 nostrils ; they communicate with an intermediate space 

 immediately above the nostrils, the latter opening 

 externally by a transverse semilunar slip. Very strong 

 muscular fibres form an expansion, which closes in the 

 upper surface of this apparatus; these fibres radiate 

 from the whole circumference of the cranium to unite 

 above the two pouches, being adapted to compress 

 them forcibly. Let us suppose the Cetacean has 

 taken into its mouth some water which it wishes to 

 eject ; it moves the tongue and jaws as if about to 

 swallow it; but closing the pharynx, the water is forced 

 up into the nasal passages, where its progress is acce- 

 lerated by annular fibres, until it raises the valve and 

 distends the membranous pouches above. Once in 

 these sacs, the water can be retained there until the 

 animal wishes to spout. For that purpose, it closes the 

 valve to prevent the descent of the water into the nasal 

 passages, and it forcibly compresses the sacs by means 

 of the muscular expansions which cover them ; and the 

 fluid, thus compelled to escape by the narrow crescentic 

 aperture, is projected to a height corresponding to the 

 force of the pressure." Intimately connected with 

 respiration or rather, we should say, with the power 

 of remaining under water for a considerable length of 

 time without respiring we find a special reservoir for 

 arterialized blood ; not formed however, by any unusual 

 enlargement of the arterial, trunks, but by a remarkable 

 extension of certain small arteries which are twisted upon 



