518 



ZOOLOGY 



SECT. 



Whalebone Whales are apparently vestiges of the femora, and 

 there may be additional vestiges representing the tibiae. 



Skeleton of Sirenia. In the Sirenia (Fig. 1163) the cervical 

 vertebrae do not coalesce, with the exception of two of them in 

 the Manatee. In the Manatee there are only six cervical vertebrae, 

 and the neural arches are sometimes incomplete. In the trunk 

 the thoracic vertebrae are numerous ; all have well-developed facets 

 for the heads of the ribs, and well developed zygapophyses. The 

 caudal vertebrae are numerous, depressed, with wide transverse 

 processes. The ribs are numerous, but few of them are connected 



Ih 



FIG. 1162. Skull of Dolphin (Globiocephalus), sagittal section, a. angle of mandible ; an. 

 external nares ; AS. alisphenoid ; bh. basi-hyal ; BO. basi-occipital ; US. basi-sphenoid ; cd. 

 condyle of mandible ; cp. coronoid process ; Ex.O. ex-occipital ; Fr. frontal ; IP. inter- 

 parietal ; ME. mesethmoid ; MX. maxilla ; Na. nasal ; Pa. parietal ; Per. periotic ; PI. pala- 

 tine ; P.Mx. pre-maxilla ; pn. posterior nares ; PS. presphenoid ; Pt. pterygoid ; sh. stylo- 

 hyal ; SO. supra-occipital ; Sg. squamosal ; th. thyro-hyal ; Vo. vomer. (After Flower.) 



with the sternum. The sternum is a broad bone not composed 

 of distinguishable segments. 



The skull (Fig. 1164) is characterised by its extreme hardness. 

 The cranial cavity is rather long and narrow as compared with 

 that of the Cetacea. Although the supra-occipital (SO.) is pro- 

 duced forwards on the upper surface of the skull for a considerable 

 distance, it does not separate the parietals (Pa.) from one another. 

 The frontals develop broad supra-orbital plates. The zygoma is 

 stout. As in the Cetacea, the external nares are very wide, but 

 they are relatively further forwards. The nasals are rudimentary. 

 The tympanic and periotic are readily separable from the other 



