GENERAL CHARACTERS 



227 



Teeth are generally present, but exceedingly variable in number. 

 In the existing species they are of simple, uniform character, all 

 having conical or compressed crowns and single roots, and are never 

 preceded by milk-teeth. They are therefore homodont and 

 monophyodont. In one group, the Mystacocetes, the teeth are 

 absent (except in the foetal condition), and the palate is provided 

 with numerous transversely placed horny laminae or "baleen." 

 The salivary glands are rudimentary or absent. The stomach is 

 multilocular, its structure being fully noticed under the genus 



Fr 



Pa 



JSO 



FIG. "5. A section of the skull of a young Dolphin (Globicephalus melas). xj. PMx, Pre- 

 maxilla ; MX, maxilla ; ME, ossified portion of the mesethmoid ; an, anterior nares ; Na, 

 nasal ; IP, inter-parietal ; Fr, frontal ; Pa, parietal ; 50, supraoccipital ; ExO, exoccipital . 

 HO, basioccipital ; Sq, squamosal ; Per, periotic ; AS, alisphenoid ; PS, presphenoid ; Pt, 

 pterygoid ; pn, posterior nares ; PI, palatine ; Vo, vomer ; s, symphysis of mandible ; id, 

 inferior dental canal ; cp, coronoid process of mandible ; cd, condyle ; a, angle ; sh, stylo-hyal ; 

 T)h, basi-hyal ; th, thyro-hyal. (From Flower's Osteology of Mammalia.) 



The intestinal canal is simple, and only in some species 

 provided with a small caecum. The liver is very little fissured, and 

 there is no gall-bladder. The vascular system is greatly complicated 

 by arterial and venous plexuses, or retia mirabilia. The larynx is of 

 peculiar shape, the arytenoid cartilages and the epiglottis being 

 much elongated, and together forming a tubular prolongation, which 

 projects into the posterior nares, and when embraced by the soft 

 palate produces a continuous passage between the nostrils and the 

 trachea, as in Ungulates, but in a more perfect manner. The 



