16 SPECIMENS OF CETACEA. 



MaxiUo-preriiaxillary Region, Rostrum, or Beak. — In Balsena the beak 

 is distinguished by its high antero-posterior arch and narrow palate, 

 from the relatively flattened dorsum and wide palate in Balsenoptera 

 and Megaptera. In Balsena the tip of the beak is pointed and formed 

 by the premaxillse ; the length of the beak is five times greater than 

 the breadth at the base : in B. musculus the side of the beak is not 

 quite straight, and the length is nearly twice the l)readth at the base : 

 in B. sihbaldi the side of the beak is more convex, the superior and 

 the premaxillfe turn inwards at the tip, and the length is about 1| 

 more than the breadth. In B. borealis the side of the beak is 

 straight, the superior and premaxillse extend directly forwards to the 

 tip ; but at its base the superior maxilla curves gently outwards ; 

 the length of the beak is rather more than twice the breadth. 

 In B. rostrata the tip is pointed, the sides are straight, the interval 

 between the premaxillae widens out to an ellipse in front of and 

 opposite the base, and the length is about If more than the breadth. 



In the above measurements, as well as in those which are to 

 follow, I have not, as is the practice with some anatomists, compared 

 the length of the beak with that of the entire skull. I have pre- 

 ferred to take the length of the beak from the tip to the notch in 

 the superior maxilla which marks the line of the base, whilst the 

 base is measured in a straight line between the opposite maxillary 

 notches. By these measurements a better idea can be formed of the 

 range in outline of the beak, from a broad triangle such as exists 

 in Orca and Globicephalus, to the long, narrow, rod-like beak in 

 Platanista. 



In Ziphius the character which at once arrests attention is the 

 dense medio-rostral bone which occupies and is fused with the 

 spout-like vomer in the interval between the two premaxillse, and 

 the length of the beak is about H times more than the breadth. 

 In Hyperoodon the medio-rostral cartilage is little if at all ossified, 

 and the length is about 2^ times more than the basal breadth. 

 In Mesoplodon the medio-rostral is ossified in the adult ; the beak 

 is more slender than in Ziphius, and its length is about 2|- times 

 more than the breadth at the base. In Platanista the beak is com- 

 pressed laterally so that the length varies in different specimens from 

 8 to 12 times more than its breadth at the base. 



In the Delphinidse the surface of the premaxillse in the beak itself 

 is not uniform. In a number of species, as Beluga, Globicephalus, 

 Grampus, L. albirostris, D. delphis, Prodelphinus, and Tursiops, it is 

 convex, a character which extends as far as or near to the tip ; in 

 Phoctena and Orcella the convexity is faintly marked ; in Monodon, 

 Cephalorhynchus, Orca, and L. acutus the premaxilla is smooth, 

 flattened, or at times faintly concave ; and in Globicephalus the pre- 

 maxilla is so broad as largely to conceal the superior maxilla. The 

 proportion of the length of the beak to the breadth at the base 

 varies with the species. In D. delphis the length is 3 times more 

 than the breadth ; in Tursio, L. acutus, Cephalorhynchus, and Beluga 

 the length is about twice greater; in Phocsena and Orca, about II; 



