566 CETACEA. 



transverse superior cranial or occipital ridge, The Delphinorhynchi are characterized, first, 



and the superior maxillary bones approach very by an extremely narrow rostrum, the length of 



close to the same part, the frontal bone seems which is four times greater than that of the 



to be represented by a very narrow osseous cranium ; secondly, by the anterior curvature 



band traversing the cranium from right to left, of the posterior extremities of the intermaxil- 

 and dilating at each extremity to form the roof laries, which, as it were, draw forwards in the 



of the orbit (c, c'). But when the maxillary same direction the maxillary, the frontal, and 



bones which have extended over the whole even the occipital bones ; thirdly, by the posi- 



anterior part of the cranium are raised, the tion of the nasal bones, which are sunk in 



frontal bone is then seen to be of much larger between the frontals and intermaxillaries ; 



size than the external appearances indicate. fourthly, by the very diminutive size of the 



The two nasal bones (d, d) are in the form temporal fossae. 



of oblong rounded tubercles, set deeply in The Delphini, properly so called, have also 



two depressions in the middle of the frontal a narrow rostrum, but its length is scarcely 



bone and in front of which the nasal passages three times that of the cranium ; the posterior 



(e e) are continued vertically downwards, extremities of the intermaxillary bones, toge- 



Th'e two intermaxillaries (/>/) form the exter- ther with the maxillary and frontal bones, are 



nal and anterior margin of the nasal apertures, raised, but not bent forwards ; the temporal 



The cribriform plate of the ethmoid consti- fossae in some species are as diminutive as in 



tutes the posterior wall of the nasal passages ; the Delphinorhynchi, but in others gradually 



and in this plate there are three or four small recede from that character, and approach, by 



perforations. The remainder of the circum- their expansion, to the form which they exhibit 



ference of the bony nostrils is formed by the in the next generic type, viz. the Inia. 



maxillary bones, of which a small part appears The cranium in this genus, besides the great 



at g : their septum is the vomer, which is extent of the temporal fossa, and the strong 



joined to the ethmoid as usual. crista which forms its superior border, is also 



The malar bone is an irregular flattened bone, characterized by the shortness of the orbital 



which assists the frontal in forming the orbit, fossa. 



and like it, is covered by the maxillary bone : In the Phocana the rostrum is as remarkable 

 it sends backwards a long and slender process, for its breadth as it is in the Delphini for its 

 which articulates with the zygomatic process narrowness ; this results from the great lateral 

 of the temporal bone, and forms the only development of the intermaxillary and max- 

 bony boundary of the lower part of the orbit, illary bones ; but the antero-posterior extension 

 The zygomatic process of the temporal bone is of the bones is diminished, and the length of 

 united to the post-orbital process of the frontal, the rostrum does not exceed that of the cranium, 

 bounding the orbit posteriorly; and thus the The Narwhals (Monodon) manifest their 

 zygomatic arch is exclusively formed by the affinity to the Porpesses (Phocana) by the 

 temporal bone : this bone terminates at the breadth and shortness of the rostrum, but differ 

 temporal ridge, having but a small extent of from that and every other genus of Cetacea in 

 development on the side of the cranium, and the development of horizontal tusks in the inter- 

 not entering at all into the composition of the maxillary bones, of which the left in the male 

 posterior convex surface. At the base of the and both in the female remain concealed in a 

 cranium the basilar and the lateral occipitals rudimental state within the maxillary bones, 

 develop expanded plates, which join the ptery- The cranium in the genus Hyperoodon, which 

 goideal alae of the sphenoid, and a lamina of includes the Great Bottle-nose Whale of Hunter, 

 the temporal bone, to which the petrous and is at once distinguishable by the remarkable 

 tympanic bones have a ligamentous attach- vertical crest which rises from the middle of 

 ment. The parietal bones also extend behind the maxillary bones, the contour of which pro- 

 the temporals, to aid in completing the basilar cess descends suddenly behind, but extends 

 walls of the cranial cavity, so that the temporal more gradually and obliquely downwards an- 

 bone is almost excluded from entering into the teriorly. The lower jaw in this genus has two 

 composition of the cranium, serving merely to rudimental teeth at its anterior part, 

 close some small vacancies left by the parietals : Lastly, in the Gangetic Dolphin (Pluta- 

 this structure is of great interest, as we perceive nista) the cranium presents a marked resem- 

 in it the commencement of that displacement blance to that of the Delphinorhynchus in the 

 of the temporal bones from the cranial parietes length and narrowness of the rostrum, and in 

 which is characteristic of the small-brained and the elevation and anterior curvature of its base; 

 cold-blooded classes of Vertebrata. but on pursuing the comparison in detail, the 

 The differences between the Dugong and structure and composition of this part of the 

 Manatee in respect to the structure of the skeleton presents several fundamental diflfe- 

 cranium, we have seen to resolve themselves rences, which at the same time indicate an 

 almost entirely into the expansion and elonga- affinity to the Cachalots fPhyseter). The 

 tion of the intermaxillary bones in relation to most striking character in the cranium of the 

 the tusks, which they are destined to support in Platanista is presented by the maxillary bones, 

 the former animal; and we shall find on a com- which, after having covered, as in the other 

 parison of the skulls of the Delphinidte toge- Delphinidtf, the frontal bones as far as the 

 ther, that they also differ from one another, temporal cristae, give off respectively a large 

 chiefly in the forms and proportions of their osseous expansion, which arches forwards and 

 maxillary and intermaxillary bones. forms a capacious vault above the spouting 



