digits have the appearance of heing thus applied, viz., the first to a single hone on
the pre-axial side of the radius ; the third to a carpal wedged in between the radius
and ulna. ; the fourth and fifth digits to the extremity of the ulna itself ; whilst the
second finger is applied to the single representative of the distal row of carpals.
In the case of a manus with six carpals, there can be little doubt that the bone
wedged between the radius and ulna is the os intermedium or luna/re, which has two
bones lying, the one external to the other on its pre-axial side. As I have shown,
these two bones are united in certain carpi, and we are, therefore, entitled to regard
the one as the scaphoid or radiale, and the other as the trapezium, a view
which appears to be fully borne out by their development. In the foetus, in which
the carpus is like a piece of cartilaginous mosaic work, each carpal element having
in its middle its little ossific centre and its limits defined by the septa of articulation,
two such distinct carpal elements, placed one before the other, intervene between the
radius and the base of the pollex. This arrangement in the foetal differs from
what I have described in the adult manus, in that these two pre-axial carpal elements
are separated from each other by a transverse, instead of a longitudinal, articulation ;
and in that the external of the two is the more anterior, and is wholly excluded from
touching the radius of itself, supporting the pollex as a true carpal in development
and form ; whereas in the adult it stretches from the metacarpal pollex to the radius
with the other pre-axial carpal element wedged in between it and the os intermedium.
As already mentioned, these two bones are occasionally fused into one in comparatively
young mani, which entitles us to conclude that in the foetal manus they were
represented only by one cartilage and ossific point. But it is when the two elements
are distinct and divided transversely, and when in that condition the more distal of
the two supports not only the pollex, but has also the metacarpal of the second finger
applied to it, that the true nature of this distal element becomes apparent. Under
these circumstances, it cannot well be regarded as a metacarpal. Eurthermore, as the
carpals for the support of the second and third fingers form two quadrangular bones at
the bases of these digits, and as the os intermedium and os radiale or scaphoid are
unmistakable, the conclusion seems unavoidable (in this aspect of things at least)
that the distal element is a trapezium. If so, it follows that when it is elongated
and reaches the radius it is also the same bone, and that the element internal toit is,
of course, the scaphoid or radiale, facts which are supported by the history of their
development, and further that a trapezio-scaphoid can: only be said to exist in
Platanista when these two elements are united in one, an abnormal occurrence in
this dolphin.
The basal free bone of the pollex would thus appear to be a metacarpal, and as
such in the six-carpaled manus is applied to the extremity of. the. trapezium, and
touches the pre-axial side of the trapezoid.
The four remaining carpal bones are all nearly of one size and more or less
quadrangular. The trapezoid projects slightly beyond the bones which support the
third and fourth digits, and is in contact with the metacarpal of the pollex, the trapezium,
the os radiale, os intermedium, os magnum, and outer edge of the third
metacarpal. The third carpal lies wholly at the base of the third digit and only
touches by its distal postaxial angle the base of the fourth metacarpal. I t is surrounded
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 radiale 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 u/nciform, 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 firmly fixed and divergent from each other, especially the
fifth, so that considerable breadth is bestowed on the manus. The pollex 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 pollex is short, but expanded at its base and contracted
at its middle. I t articulates with the variously modified trapezium and
with a very restricted angle of the trapezoid. I t 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
is in contact with its fellows of the third and fifth digits, and has its base
supported entirely 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.
Musculo- tendinous structures o f 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 dissections
of Elower1, Carter and Macalister8, Perrin*, and Struthers4. Previous writers
1 Pros. Zool. Soc. Lond., 1865, p. 705.
3 Trans. Royal Soc, Loud., 1868, p. 228.
3 Pros. Zool. Soc. Lond., 1870, p. 811.
4 Journ. Anat. and Phys., vol. vi, 1872, p. 110, et ib id s vol. viii, 1874, p. 112.