340 THE ANATOMY OF VERTEBRATED ANIMALS. 



h. In tlie Delphiyioidea the nasal chambers open by onl;^ 

 a single spiracle on the top of the head; and saccular dilata- 

 tions of various dimensions are developed from the walls of the 

 passage which connects this aperture with the bony naso- 

 palatine passages, and lie between the integument and the 

 outer surface of the skull. 



More or fewer of the anterior ribs have heads and necks, 

 the capitula articulating with the bodies of the vertebras, as 

 (n other 3Iammalia. The elongated sternum is, almost al- 

 ways, composed of several pieces arranged in a longitudinal 

 series ; and cartilaginous, or ossified, sternal ribs are present 

 in greater or smaller number. The nasal bones, which are 

 very short, and have their upper surfaces tubercle-like, are 

 more or less asymmetrically developed, as are also the max- 

 illas ; so tliat the facial part of the skull appears distorted. 

 The maxillae are expanded behind, and cover the orbital pro- 

 cess of the frontal bone wholly or partially. The lachrymal 

 bone is usually small and confluent with the slender jugal, but 

 it may be large and distinct. The rami of the mandible are 

 not arcuated outward, and they become united in a longer or 

 shorter symphysis. The mandible, as a whole, is not sensibly 

 broader than the corresponding portion of the maxillo premax- 

 illary part of the skull. 



Teeth always exist after birth, and are never replaced by 

 baleen plates. They are usually numerous, but sometimes few 

 and deciduous. Occasionally, only one or two teeth persist, 

 and these, as in the Narwhal, may take the form of immense- 

 ly-elongated tusks. 



To this division belong the Physeteridce JPlatanistidm and 

 Delphinidm. 



The Physeterid'X possess functional teeth only in the Ioav- 

 er jaw. The asymmetry of the skull is strongly pronounced ; 

 and, in the adult, the maxillary and frontal bones are pro- 

 duced, so as to form a sort of basin upon the upper and ante- 

 rior surface of the skull. The pterygoids meet in the middle 

 line below, and the mandibular symphysis is sometimes ex- 

 tremely long. 



The crreater number of the cervical vertebras are ancliy- 

 losed. The hinder ribs lose their tubercular, but retain their 

 capitular articulation with the vertebras. The costal carti- 

 lages are not ossified. The pectoral limbs are small, and a 

 dorsal fin is usually present. 



The proper Sperm Whales (Physeterinm) have an enor- 

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



