518 General Notes. | May, 
the shoulder and hip-girdles. Manifestly the pes of a form like 
Megaptera, if mobile, would require a system of phalanges as 
powerful as those in the manus, but the pes is not mobile in any 
cetacean, on its own base, as is the fore-limb, but is rigidly affixed 
to the sides of the end of the tail and incapable of independent 
movement, hence the atrophy of its bones. The only evidence 
remaining to indicate that the pedes or flukes of cetaceans were 
once possessed of well-developed phalanges, is the distribution 
of the dorsal and ventral interdigital arteries, the arrangement of 
these in fact indicating that there was a great inequality in the 
length of the digits of the pes, the same as we now see in the 
manus, thus leading to the conclusion that the foot-structure of 
the ancestral or protocetacean type was so far different from that 
of the pinnipeds. 
the tail, which, with the total abandonment of the land by the 
animal, would become stronger and its centra greatly developed, 
carrying the pedal folds or flukes still farther rearward, and 
thus increase still more the interval between them and the rem- 
nants of the pelvis. At the same time, the muscles of the tail 
would become greatly developed, so that in the cetaceans we 
actually have the spectacle of an animal type which has descended 
from a land form with a degenerate tail again acquiring a tail of 
the functional importance of that of a fish, but structurally very 
dissimilar, especially as regards the arrangement of its muscles, 
which are not homologous with the muscular somites of a fish’s 
tail. The pes thus becomes the only outwardly apparent part of 
the hind limb, just as the manus is the principal part exserted in 
the fore-limbs of cetaceans, where some of the muscular inser- 
tions have also been shoved outward or into a more distal an 
effective position. The inclusion of the end of the tail of ceta- 
ceans between the flukes has also differentiated the caudal verte- 
brz of the latter into two distinct and well-marked series, so that 
the centra, as respects their vertical diameters, do not taper from 
the sacral region backward, as in other mammals, but only from 
in front of the flukes backward. ; 
-he arrangement of the vessels of the manus and flukes is 
