4IO CLASSIFICATION OF VERTEBRATES. 



consists of large numbers of cornified papillae arising from the ectoderm 

 lining the cavity of the mouth. 



In the BAL^NOPTERID^: the head is less than a fourth of the total body 

 length, the ventral side of the body is usually marked by longitudinal grooves, 

 a dorsal fin (a tegumentary fold without skeleton) is present, the hands have 

 four digits, and the cervical vertebras have their large centra free. Balirnop- 

 tera.i with the head small and flat, and the grooves extending back as far as 

 the throat region, contains the rorquals, fin-backs, or razor-backs. B. sib- 

 bahii is the largest whale, reaching a length of 85 feet. Megaptera includes 

 the hump-back whales. The family occurs in all rocks since the miocene. 

 The BAL^ENID^ or right whales date only from the pliocene ; they have a 

 large head, the ventral surface smooth, the hand pentadactyl, the cervical 

 vertebras fused, and no dorsal fin. Bahrna, Neobalana, and Rhachianectes 

 belong here. 



ORDER VIII. CARNIVORA (FER^E). 



Terrestrial or aquatic flesh-eating mammals with unguicu- 

 late four- or five-toed feet ; incisors usually , canines |, strong, 

 pointed and recurved ; molars more or less sectorial ; mammae 

 abdominal ; placenta decicluate, almost always zonary. 



The carnivora receive their name from their flesh-eating 

 habits, but it must be understood that not every species con- 

 forms to this rule, since some live largely upon a vegetable diet. 

 All have diphyodont and heterodont dentition ; the first incisor 

 is smallest, the third largest. The canines are especially charac- 

 teristic ; the premolars are compressed and are usually sectorial, 

 while the molars are occasionally broad, but still have cuspidate 

 crowns. The milk dentition is usually functional for a year after 

 birth. 



The feet have either four or five toes, and may be either 

 plantigrade, semiplantigrade, digitigrade, or in the seals modi- 

 fied into flippers. The claws are usually compressed, but occa- 

 sionally may be rudimentary or absent. In the living species 

 the brain is large and richly convoluted, but in the creodonts it 

 was much smaller and nearly smooth. The stomach is a simple 

 pear-shaped sac ; the caecum is small or absent ; the uterus two- 

 horned. The radius and ulna are always distinct, the fibula 

 .always slender. 



Through the extinct group of creodonts the carnivores are 

 closely related to the insectivores, and possibly to the marsupials. 

 In fact Cope has taken the creodonts and united them with in- 



