ribs to the sternum having ever been separated, and the perfect sternum being quite
intact. I t is significant that this sternum belongs to a skeleton with rib-like
processes attached to the superior process of the seventh cervical vertebra, and it
would thus appear that the presternum was involved in the same abnormality that
produced this imperfect rib.
The first section of the mesosternum is about two-thirds of the length of the
presternum, is shortly oblong in form, and much dorso-ventrally compressed, with
concave but rounded lateral margins. I t is perfectly flat internally, and very slightly
concave from side to side externally, but somewhat concave from before backwards.
Its anterior and posterior extremities are rather deeply notched in the
middle line, the notch corresponding to the remains of a faint indication of the
original suture between the two portions of which it is composed. The right half is
considerably larger than the left.
The second rib generally articulates between the prestemum and first section of
the mesosternum, but in the youngest example before me, the attachment of the
second rib is behind the ossicle of the first segment of the mesosternum; whereas
in the mother of this specimen it is in the normal position. The hinder angles of
the segment have each a hollow for the attachment of the third sternal rib.
The presternum and mesosternum are separated from each other in the young by a
considerable cartilaginous space, but they frequently unite even in adolescence.
The second segment of the mesosternum consists of two distinct ossicles separated
from each other and from the first section, in youth, by a wide cartilaginous interval
which afterwards disappears, the two ossicles becoming thoroughly amalgamated,
and in adults they nearly equal the length of the first section. The fourth rib
is applied to the extremity of this ossicle. Only four ribs thus directly articulate
with the sternum as a whole. The xiphoid cartilage is rather large and lingulate
in the young, but never presents any trace of ossification.
Scapula (PI. XLI, fig. 13).—This bone is fan-shaped and, as Cuvier remarks,
“ est beaucoup plus large qu’au dauphin.” Its depth through its middle
(glenoid) is three-fifths of its greatest length. The postscapular fossa is absent,
the external surface being smooth and slightly convex. The suprascapular border
is long and forms nearly the half of an elongated oval, defining a nearly triangular
surface with the posterior border which is almost straight, the two meeting in a
point. The anterior margin is divided into two deep notches by the large acromion
which, in adults, developes a metacromia! process directed upwards, the acromion
pointing reversely downwards. The capacity of the upper or supra-metacromial
notch is variable, even in the scapulae of the same individual, which is also the case
with the acromio-coracoid notch. The metacromial process is also variable in its
intensity in the same individual, but there is no trace of it in very young dolphins
; neither does the ossification of the coracoid show itself in early life. The
latter is a mere rudiment, being little more than a small pointed nodule rising about
half an inch above the glenoid articulation, which is more oval than round and
in this very different from Rontoporia. The outer surface is marked by a ridge running
up from the coracoid to the suprascapular border, terminating in a faint notch,
one inch posterior to the anterior angle of the suprascapular border, and indicating
the position of the mesoscapula and defining a slight fossa in front of it. The pleural
surface corresponding to this ridge is ^he most convex portion of the scapula. There
is another slight ridge-like convexity prolonged upwards from on a line with the
posterior glenoid border, but not continuous with it. The bone anterior to this is
convex from before backwards, so that the interval between these ridges would
seem to indicate the existence of a broad mesoscapula.
Humerus (PI. XLI, fig. 14, h).—The length of this bone nearly equals
the united extreme lengths of the antibrachium and carpus. The latter again are
equivalent to the metacarpal bone and first phalanx of either of the first, second or
third digits. The extreme breadth of the humerus at the radio-ulnar joint is two-
thirds of its own length. The narrowest part is immediately below the neck and is
more than one-third of its length. The base is antero-posteriorly compressed from
the neck to the radio-ulnar joint, where it expands into two nearly equal radial and
ulnar surfaces, forming an obtuse angle with one another in the middle line, the
external being sharp and longer than the internal margin, which is short thick and
concave. The globular head is defined by a well-marked constriction, which, however,
does not extend round the external surface, although there is little, if any,
motion at the elbow joint. I have never observed the humerus to anchylose with
the radius and ulna.
Radius.—This bone (f) is much flattened and has a convex sharp external
border, which is imperfectly ossified in young specimens. Its inner border is short;
and concave, corresponding to the short but elongately oval interspace that exists
between the two bones of the antibrachium. By its distal extremity it articulates
with three bones of the carpus, by the two nearly equal surfaces that meet in an
obtuse angle.
Ulna.—This bone (u) is flattened, broader than long at its distal extremity and
slightly shorter than the radius, and has both of its lateral borders concave, its
rlistfll end expanding into two obliquely-placed surfaces, the proximal of which is
much the smaller of the two and concave.
Bones o f carpus (PL XLI, fig. 14).—These are generally six in number,
but they are subject to great variation even in the same individual, amalgamating
with each other and with the ulna, and so being occasionally reduced to three. I t
does not appear that the fusion is the result of anchylosis dependent on old age,
because it has as yet been observed only in comparatively young animals.
In carpi with six bones, there are three in the proximal row in contact with the
radius,—in the distal row one at the extremity of the ulna and common to the fourth
and fifth digits; the remaining two are at the base of the second and third digits.
Sometimes the two bones on the pre-axia! side of the radius (rd and tin) partially or
wholly unite, the os intermedium (pi) amalgamates with the carpal (mg) at the
base of the third digit, and the bone (cu) supporting the fourth and fifth digits
coalesces with the ulna. This condition gives only three carpal bones. Hence the: