400 THE ANATOMY OF VERTEBRATED ANIMALS. 



few and deciduous. Occasionally, only one or two teetli 

 persist, and these, as in the Narwhal, may take the form of 

 immensely elongated tusks. 



To this division belong the Physeteridce, FlatanistidcB and 

 Delphinidce. 



The -Physeteridce. possess functional teeth only in the 

 lower jaw. The asymmetry of the skull is strongly pro- 

 nounced ; and, in the adult, the maxillary and frontal bones 

 are produced, so as to form a sort of basin xipon the upper 

 and anterior surface of the skull. The pterygoids meet 

 in the middle line below, and the mandibular symphysis 

 is sometimes extremely long. 



The greater number of the cervical vertebras are anky- 

 losed. The hinder ribs lose their tubercular, but retain 

 theii' capitular articulation with the vertebrae. The costal 

 cartilages are not ossified. The pectoral limbs are small, 

 and a dorsal fin is usually present. 



The proper Sperm Whales {Physeterin<e) have an enor- 

 mous head, with a quadrate, truncated snout, at the anterior 

 superior angle of which the spiracle is placed. The teeth 

 become fully developed only in the lower jaw. The cranial 

 basin is immense, and is filled by a loose connective tissue, 

 in which the peculiar fat known as spermaceti is contained. 

 Ambergris is a sort of bezoar, found in the alimentary 

 canal of the Cachalot, and seemingly derived from the fatty 

 matter contained in the Cephalopoda on which the Cetacean 

 feeds. In the other group of the Physeteridce- — the Ziphiince 

 or Bhynchoceti — to which the Bottlenosed Whale (Hyperoo- 

 don) belongs, there are only one or two pairs of fully f oi-med 

 teeth in the mandible. Some recent and many fossil 

 (middle and later tertiary) genera of these Cetaceans are 

 remarkable for the elongated rostrum formed by the solid 

 ossification and ankylosis of the ethmoid, premaxillas and 

 maxillae. 



The Platanistidce are fluviatile or estuarine Cetacea, which 

 occur in the Ganges and in the I'ivers of South America. 

 The cervical vertebrae are not ankylosed, and the costal car- 

 tilages are not ossified. The tubercula and capitula of the 



