354 MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 
and 25" in greatest diameter at the proximal end; the other is 11” in length, and 25” 
in diameter at the same point. 
The ribs of the Caithness and Yorkshire skeletons agree in their number and general 
characters with those of the present specimen. In the former, the two rudimentary 
eleventh ribs are preserved, and are 13’ and 12}” long respectively, and somewhat 
stouter than in the Tasmanian Cachalot. In the skeleton at Burton Constable they are 
not present; but the condition of the ends of the transverse processes of the corre- 
sponding vertebre clearly indicate their former existence. In the Sydney skeleton, ten 
pairs of fully developed ribs are described. The small eleventh pair, if they existed, 
may easily have escaped observation, especially as the animal was scarcely more than 
half-grown. 
The skeleton at Paris has fourteen pairs of large ribs, with indications on the trans- 
verse processes of a fifteenth. Their articular surfaces, as well as the corresponding 
processes of the vertebra, are much decayed and broken; but, as far as can be ascer- 
tained, they appear to follow each other in a regular and natural sequence, and afford 
no certain evidence that the skeleton has been artificially compounded. ‘The first pair 
have rudimentary capitular processes, larger on the left than the right side. ‘These 
are followed by ten pairs with well-developed capitular processes reaching to the bodies 
of the vertebre in the usual way. The last three are connected only with the lower 
transverse processes, which are strongly developed and hollowed out at the end for 
their reception. 
In all the true Dolphins (Delphinide) the anterior ribs (about half of the series) have 
long heads, by which they are connected with the body, or root of the arch, of the ver- 
tebra in front of that to which the tubercle is attached. Near the middle of the series 
this head suddenly ceases to be developed, and the ribs articulate only to one vertebra, by 
the tubercle. It will be seen from the preceding description that in the Cachalot the 
condition of the upper end of the ribs, and their mode of connexion with the vertebre, 
is quite different. Of the Cetaceans whose osteology is thoroughly known, Hyperoodon 
comes nearest to Physeter in this respect, as already mentioned when speaking of the 
transverse processes of the thoracic vertebra. ‘The form of the first rib of the Cachalot, 
however, is very peculiar—the absence of a distinct head reaching the body of the 
vertebra having no counterpart among Toothed Whales, not even in Hyperoodon. 
Sternum. 
The sternum (Pl. LX. figs. 3 and 4), is a large, massive bone, though of rather spongy 
texture. Its general form is roughly triangular, the apex being turned backwards. 
The broad anterior edge, nearly equal to the sides in length, is tolerably straight. It 
is composed of three distinct portions—two large anterior lateral pieces, and a small 
posterior median piece. The former have probably each consisted of an anterior and 
posterior portion, though the traces of this distinction are well-nigh obliterated. The 
