48 Mammalia. Sirenia. 



are distinguislied bj the ' chevron bones,' viz., haera apophyses 

 articulated in Cete, as in Crocodilia, directly to the under surface 

 of the centrum and coalesced at the opposite ends, thus forming 

 a haemal canal analogous to, but not homologous with, that in 

 Fishes. The Caudal vertebrae of Whales farther differ from those 

 in Fishes, in retaining the transverse processes, and in becoming 

 flattened from above downwards without coalescing. 



Aiiterior Appendages. The Anterior Limbs alone are developed, 

 and are flat and fin-like. The Clavicles are wanting. The Scapula 

 is broad, flat, and without a spine along the outer surface; it has 

 a short stunted Coracoid anchylosed to it, and is freely suspended 

 in the flesh {cf. Fish). The Humerus is remarkably short in propor- 

 tion to its thickness, as in most Aquatic Mammalia. There is no 

 complete articulation between the bones of the Fore-arm and the 

 Humerus. The Olecranon, though generally present, is but slightly 

 developed. The two short bones* of the Fore-arm lie immoveably 

 behind each other, and are very flat. There is no complete articu- 

 lation between the bones of the Carpus, Fore-arm and Digits. The 

 Carpal bones are generally three to five in number, dice-shaped, and 

 lying between thick tendons and masses of ligament. Some of the 

 Digits have more than three phalanges ; in the Whales five to six, and 

 in the Dolphins even more. All the Digits in the natural state are 

 enveloped in a common fold of integument. The increase of the 

 Phalanges of certain Digits beyond the number three is a remarkable 

 instance of departure from the Mammalian type, and of affinity 

 with the extinct En-alio-saurus and Fishes. 



Posterior Appendages. The Pelvic bones consist of two simple 

 elongated bones, lying near the anal and generative organs, which 

 converge together from opposite sides, or are connected by a trans- 

 verse piece: these traces of Innominate hones are remote from the 

 vertebral column and connected with the rest of the skeleton by 

 muscles only. There is never more than a trace of hind limbs; 

 these, when found, are represented [{e.g. in the Eight Whale) by a 

 two-jointed ray. This is the simplest condition of the limb, or ap- 

 pendage, of the Pelvic Arch known in the Mammalian Class. 



XII. SIRENIA. 



All the bones of the skeleton are solid. 



The Skull. The Facial, or rostral parts of the skull, anterior to 

 the orbits, is short. All the skull bones are massive, and, save in 



