CETACEA. 



567 



apparatus of the nostrils. In order to consti- 

 tute this part, one of the processes inclines 

 towards the other, so as almost to come in 

 contact with it for the two anterior thirds ; but 

 posteriorly they recede from one another to give 

 passage to the blow-hole. The cavity beneath 

 this singular bony pent-house is occupied by 

 an interlacement of numerous osseous pro- 

 cesses, and by a close and hard fibrous sub- 

 stance.* 



If we suppose the cranium of a Dolphin 

 to be proportionally very much shortened, the 

 margins of the rostrum to be greatly expanded 

 and raised, so as to render its superior 

 surface concave; the supra-frontal portions 

 of the maxillary bones to be much developed 

 and the margins extended upwards, thus form- 

 ing an immense basin, at the bottom of which 

 lie the external orifices of the bony nostrils ; 

 if also the occipital crest in the Dolphin were 

 raised behind the maxillaries so as to aid them 

 in the formation of the bony cavity, in the 

 basis of which the parietals are almost con- 

 cealed, we should then have the skull of a 

 Cachalot. The rostrum in the Catodontidae, not- 

 withstanding its immense size, is formed prin- 

 cipally by the maxillary bones, as the inter- 

 maxillaries and the vomer constitute a compa- 

 ratively small part of the intermediate portion. 

 The nasal passages extend obliquely from below 

 upwards and forwards, but are of very unequal 

 dimensions, the one on the right side not 

 having one-fourth the breadth of that on the 

 left. A corresponding want of symmetry is 

 shown in the nasal bones themselves, and the 

 cranium generally; and this circumstance, it 

 may be remarked, characterizes in a greater 

 or less degree the skull in all the Zoophagous 

 Cetacea. 



The skull in the Whalebone-Whales (Bala- 

 nid<z) is, however, the most symmetrical in its 

 general form; it is characterized by the great 

 relative predominance of the facial over the 

 cranial portion, by the narrowness of the ros- 

 trum, and the curvature of the rami of the lower 

 jaw, which each extend outwards, in a convex 

 sweep, far beyond the sides of the upper max- 



illa, and converge to the symphysis, but with- 

 out meeting to form a bony union at their ante- 

 rior extremities. 



In the Mysticete, or common Whalebone- 

 Whale (of which a side view of the skull is 

 given at)%. 249) the immense maxillary bones 

 (a, a) are compressed, and disposed each like 

 an expanded arch along the outside of the in- 

 termaxillaries (b) and the vomer; their inferior 

 surface has two facets separated by an interme- 

 diate longitudinal ridge, to the sides of which 

 the plates of whalebone or baleen are attached 

 (b,fig. 259). The intermaxillary bones are also 

 laterally compressed, and diverge from each 

 other posteriorly to form the long elliptical 

 bony out'et of the nostrils; this orifice is com- 

 pleted behind by the nasal bones, which are of 

 very small size, and are partially covered by 

 the frontal bones, which project forwards above 

 them in the form of two small points. The 

 tranverse portions of the frontal (c) and max- 

 illary (a*) bones, which contribute to form the 

 orbits, extend obliquely backwards : the tem- 

 poral bone (d) is of an irregular quadrate 

 form, and extends much further backwards 

 even than the occipital condyles. The occipital 

 bone (e) advances forwards so as to cover 

 almost all the upper part of the cranium, 

 where it presents a general convexity. Each 

 ramus of the lower jaw (f) is convex exter- 

 nally, compressed and somewhat trenchant 

 both at the upper and lower margins. The 

 coronoid process, on which the letter is placed, 

 is in the form of a slightly raised obtuse angle ; 

 the condyloid process (g) forms the large tube- 

 rosity behind. It is articulated to the glenoid 

 cavity by a mass of ligamentous fibres, and not 

 by a capsular ligament surrounding a synovia! 

 cavity. 



The vertebral column of the Cetacea does not 

 differ from that of other mammalia except in the 

 modifications demanded by their peculiar mode 

 of existence. The cervical vertebrae, of the 

 normal number of seven, with the exception 

 of the Manatee, are in general extremely thin, 

 and though in some species, such as the 

 Manatee, the Dugong (k, Jig. 246), and the 



Fig. 249. 



* For a detailed account of the structure of the 

 skull in this singular fresh-water Cetacean, see 

 Cuvier, Ossemens Fossiles, v. pt. i. p. 298. 



Platanista, they are found free; others, as the 

 Dolphins and Porpesses, have the first two 

 commonly anchylosed together. In the Balae- 



