XVI.] SIRENIA. 275 



extremity ; the digits being nearly equally developed, spread- 

 ing from each other, and without any excessive number of 

 phalanges. In the Grampus {Orca) all the phalanges are 

 broader than they are long.^ In the Round-headed Dol- 

 phins {Glohiocephalus, Fig. 09), on the other hand, the manus 

 is extremely elongated, narrow, and pointed. This elongation 

 is mainly due to the great development of the second, and, 

 though to a less extent, of the third digit; the fourth and 

 fifth being quite short, and having but few phalanges. The 

 number of phalanges (including the metacarpals) in the 

 different digits are respectively I. 4, II. 14, III. 9, IV. 3, 

 and V. I. 



In the common Dolphin {Delphinus) the manus has the 

 same essential form, though in a less exaggerated de,^ree, 

 the numbers of the phalanges being I. 2, II. 10, III. 7, IV. 3, 

 and V. I. The digits are all in close contact. 



Order Sirenia. — Though in external form, and in being 

 enclosed in an undivided integument, the terminal segment 

 of the fore limb of the animals constituting this order 

 much resembles that of the Cetacea, its skeleton is totally 

 different. 



The carpus is short and broad. In the genus Manatus 

 the seven most usual bones of this region are all distinct, 

 though there is no pisiform. The trapezoid is very small, 

 and placed almost on the dorsal surface of the trapezium. 

 The cuneiform is large, and supports the greater part of the 

 fifth metacarpal. In Halicore many of the bones of the 

 carpus usually coalesce ; thus the first row may consist of 

 two bones, a scapho-lunar and a cuneiform, and all the 

 bones of the second row may unite together. 



In both genera the digits are five in number, with 



This genus is remarkable for the imperfect ossification of the carpal 

 bones. 



T 2 



