INTRODUCTION. 17 



in Monodon, Orcella, Grampus, L. albirostris, about IJ- ; and in Globi- 

 cephalus the length is about IJ more than the breadth at the base. 



The Pterygoids and Hard Palate. — In the Baleen Whales the 

 pterygoids are small and separated mesially by a wide cleft ; the 

 palate plates of the palate bones are large. In Physeter, Hyperoodon, 

 Ziphius, and Mesoplodon the pterygoids are large and meet mesially. 



In an important memoir Sir Wm. Flower pointed out (Proc. Zool. 

 Soc, 1883) the characters of the pterygo-palatal region in the classi- 

 fication of the Delphinidae, and subsequently Mr F. W. True, in his 

 Review of the Delphinidte, has gone over the same ground. It may 

 be sufficient, therefore, if I confine myself to a brief statement of 

 the characters observed in the skulls in the Anatomical Museum. 



The hinder end of the hard palate is formed by the pair of 

 pterygoids situated immediately behind the palate plates of the 

 palate bones ; each is hollowed into a sinus opening backwards. 

 They lie in the same transverse plane, but their relations to the 

 middle line vary with the species. Thus, in Beluga, Cephalorhynchus, 

 Phoceena, Orcella, and in some skulls of Orca they are separated by 

 a wide cleft ; in Globicephalus, and sometimes in Orca, the interval 

 is a narrow fissure ; in Monodon, Grampus, L. albirostris and acutus, 

 Delphinus, Tursiops, they meet mesially and complete the hard 

 palate behind. The palatal plate of the palate bones in Globi- 

 cephalus, Phocccna, Delphinus sends a process backwards which 

 intervenes between the more anterior half of the inner borders of 

 the two pterygoids. 



The hard palate is chiefly formed by the pair of superior maxillae 

 which usually articulate in the middle line. Sometimes, as in 

 Physeter, Hyperoodon, Ziphius, Mesoplodon, Tursiops, Lagenorhyn- 

 chus, Prodelphinus, they do not meet mesially in their whole length, 

 and allow the lower edge of the vomer to appear. The premaxillae 

 are only visible in the palate near the tip. In the Baleen Whales the 

 palate is perforated by large foramina for the blood-vessels and nerves 

 which supply the folds and papillpe on the mucous membrane, from 

 which the baleen plates are developed and grow. In Balsena the 

 palate has a strong keel in the middle line, which is not so marked 

 in Balsenoptera. 



Delphinus, as the genus is now limited, is distinguished from 

 other Delphinidse by a mesial palatal ridge and a wide, deep longi- 

 tudinal groove on each side of the ridge. 



Teeth. — It is now recognised that in the Cetacea generally 

 rudiments of teeth are formed in the gums of the foetus. In the 

 Mystacoceti they disappear at an early stage, never cut the gum nor 

 possess functional value. In the Odontoceti, again, the teeth 

 develop and acquire functional importance. As a rule, the teeth 

 are small, conical in shape, and have the same form in whatever 

 part of the jaw they are situated, tliough sometimes they assume 

 specific characters. In Layard's Me?oplodon, for example, a pair of 

 mandibular teeth grow to form broad, strap-like fangs of great size 

 which enclose the beak of the upper jaw. In Sowerby's Whale a 



