502 



ZOOLOGY 



SECT. 



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synovial articulation. In 

 the Cetacea there are some- 

 times five digits, sometimes 

 only four : more or fewer 

 have considerably more 

 than the normal number 

 of phalanges, sometimes as 

 many as fourteen. The 

 second is usually the longest. 



Vestiges of the pdms are 

 present in the form of a 

 pair of long narrow bones 

 (Fig. 1079, pelv.) which lie 

 parallel with the spinal 

 column some little distance 

 below the region where the 

 chevron bones begin. These 

 appear to represent the 

 ischia. A second pair of 

 smaller bones which lie close 

 to these in the Whale-bone 

 Whales are apparently ves- 

 tiges of the femora. 



Skeleton of Sirenia.- 

 In the Sirenia (Fig. 1082) 

 the cervical vertebra never 

 coalesce, with the exception 

 of two of them in the 

 Manatee. In the Manatee 

 there are only six cervical 

 vertebra?, and the neural 

 arches are sometimes in- 

 complete. In the trunk 

 the thoracic vertebras are 

 numerous ; all have well- 

 developed facets for the 

 heads of the ribs, and well- 

 developed zygapophyses. 

 The caudal vertebra? are 

 numerous, depressed, with 

 wide transverse processes. 

 The ribs are numerous, but 

 few of them are connected 

 with the sternum. The 

 sternum is a broad bone not 

 composed of distinguish- 

 able segments. 



