PLATANISTA. 541 



metacarpal. The third carpal lies wholly at the hase of the third digit and only 

 touches hy its distal postaxial angle the base of the fourth metacarpal. It is sur- 

 rounded by the second carpal, os intermedium, and the fourth carpal which supports the 

 fourth and fifth digits, and has its distal and postaxial sides applied to the fourth and 

 fifth metacarpals respectively, its proximal to the ulna, and its pre-axial to the third 

 carpal. The os intermedium has the third carpal applied to its distal side and its pre- 

 axial and postaxial surfaces articulating with the os radiate and ulna respectively, 

 while its proximal side is in contact with the radius, its postaxial and pre-axial angles 

 touching the fourth carpal and also the os trapezoid. 



The bone at the extremity of the ulna supporting the fourth and fifth digits 

 would appear to represent the cuneiform and unciform, although it is developed from 

 only one ossific centre. A similar uncertainty attaches to the morphology of the so- 

 called OS intermedium and os magnum, because it is possible that one or other may 

 contain an os centrale, although there is nothing in the character of the foetal manus 

 to favor such an hypothesis, as each originates from a single ossific centre. 



The phalanges are fiirmly fixed and divergent from each other, especially the 

 fifth, so that considerable breadth is bestowed on the manus. The poUex is only little 

 more than one-third of the length of the forefinger or second digit, which is slightly 

 larger than the other three, these being almost equally long, the fifth, if anything, 

 somewhat shorter than the fourth. 



The metacarpals are more or less compressed from behind forwards, a character 

 which is much more marked in the phalanges, the distal ones being flattened oval 

 ossicles. The metacarpal of the poUex is short, but expanded at its base and con- 

 tracted at its middle. It articulates with the variously modified trapezium and 

 with a very restricted angle of the trapezoid. It is furnished with one well-ossified 

 phalanx tipped with cartilage containing a small ossicle. The second metacarpal is 

 supported by the trapezoid only, and is contracted in its shaft and expanded at its 

 ends, being supported almost entirely by the third carpal, although it touches by the 

 angles of its base the trapezoid and the fourth metacarpal. The latter in a similar 

 manner is in contact with its fellows of the third and fifth digits, and has its base 

 supported entkely by the probably complex cuneiform, which also carries by its 

 postaxial side the fifth metacarpal, thus resting as well on the ulna. 



The phalanges in the perfect manus are, 2, 5, 5, 5, 5, and they are longer than 

 broad, with their shafts contracted in the middle and expanded at their ends. The 

 distal phalanges are generally small ossicles in the cartilaginous tips of the fingers. 



Muscuto-tendinous structures of the manus (Wood-cuts, figs. 19 and 20). — It 

 is only within the last few years that representatives of flexors and extensors of the 

 manus of Cetaceans have been demonstrated. This has been due chiefly to the dissec- 

 tions of Plower*, Carter and Macalister^ Perrin\ and Struthers*. Previous writers 



1 Pros. Zool. Soc. Lond., 1865, p. 705. 



2 Trans. Royal Soc. Lond,, 1868, p. 228. 



3 Pros. Zool. Soc. Lond., 1870, p. 811. 



'* Journ. Anat. and Phys., vol. vi, 1872, p. 110, et ibid ; vol. viii, 1874, p. 112. 



