THE DELPHINOIDEA. 399 



cricoid cartilage and the rings of tlie trachea are incom- 

 plete in front, and a large air sac is developed in the 

 cricothyroid space. The Balcenoidea possess olfactory- 

 nerves and a distinct, though small, oKactory apparatus. 

 The sclerotic coat of the eyeball is enormously thick, and 

 the optic nerve is surrounded by a rete-mirabile. The tym- 

 panic membrane is connected with the malleiis by ligament. 

 The semicircular canals are very small, but the cochlea is 

 large, and makes only Ij turns. The muscles of the 

 antebrachium and manus are not altogether absent. 



The Right Whale {Balcena), and the Fin-fishes (Mega- 

 ptera, Balcenoptera, &c.), belong to this division. 



h. In the Delpliinoidea the nasal chambers open by only 

 a single spiracle on the top of the head; and sacciilar 

 dilatations, 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 integu- 

 ment and the outer surface of the skull. 



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

 the capitxila articulating with the bodies of the vertebrae, as 

 in other Mammalia. The elongated sternum is, almost 

 always, composed of several pieces arranged in a longi- 

 tudinal series ; and cartilaginous, or ossiiied, 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 maxillse ; so that the facial part of the skull appears 

 distorted. The maxillse are expanded behind, and cover 

 the orbital process of the frontal bone wholly, or par- 

 tially. The lachrymal bone is usually small and confluent 

 vrith the slender jugal, but it may be large and distinct. 

 The rami of the mandible are not arcuated outwards, and 

 they become tmited in a longer, or shorter, symphysis. 

 The mandible, as a whole, is not sensibly broader than the 

 coiTCsponding portion of the maxillo-premaxillary part of 

 the skull. 



Teeth always exist after birth, and are never replaced by 

 baleen plates. They are usually numerous, but sometimes 



