MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 353 
following changes may be observed gradually occurring in them. They become more 
slender and rounded in the middle part of the shaft. The capitular process becomes 
slightly shorter, but at the same time thicker; and the capitulum itself becomes larger 
and more irregular in shape. The tubercle becomes rather less prominent. ‘The 
inferior end of the rib presents a less marked enlargement, and is more regularly 
cylindrical. 
Each of these ribs articulates in the usual way by the tubercle with the transverse 
process of the corresponding dorsal vertebra, and by the head with the facet on the 
hinder edge of the body of the preceding vertebra. ‘The last two may also have had a 
slight connexion with the body of the corresponding vertebra. 
The seventh rib has a shorter but very thick neck, the capitular surface of which is 
produced backwards, so that it articulates distinctly with the bodies of two vertebre, 
chiefly, however, with the one in front of that to which its transverse process is 
attached. The articular surface of the tubercle is much elongated in the fore-and-aft 
direction. 
The eighth repeats much the same condition at the upper end; it may be distin- 
guished, however, by its greater slenderness, especially at the lower end, which presents 
scarcely any appreciable enlargement. 
The form of the upper end of the ninth rib is very characteristic. The neck is still 
shorter than in the last, and very obliquely truncated ; but its articular surface is large, 
and, contrary to what obtains in the preceding, particularly so at the hinder part, as it 
articulates chiefly with the raised facet on the body of its own vertebra. The tubercle 
is large and overhangs the posterior hollowed surface of the capitular process. Below 
the tubercle the rib is very slender, and has a slight twist backwards. The lower part 
is flattened from without inwards, and has a prominent sharp ridge on the posterior 
margin. 
The tenth rib is considerably shorter than the ninth. The capitular process is 
entirely absent; but the expanded upper end, which articulates only with the end of 
the transverse process of the tenth dorsal vertebra, is divided by a vertical groove into 
two unequal surfaces, of which the anterior larger one represents the base of the neck, 
and the smaller posterior one the tubercle. The lower end is flattened and twisted 
somewhat backwards. 
The eleventh rudimentary pair of ribs are nearly straight, the longer one having a 
slight sigmoid curve. They are largest at their attached extremity, and gradually taper, 
but are slightly enlarged again at the tip. In the greater part of their length they are 
flattened from above downwards; but, having a slight twist on their own axis, the longest 
one becomes towards its distal extremity flattened almost in the opposite direction. The 
proximal ends are truncated, having an oval, slightly convex articular surface, which 
was tipped with cartilage. ‘These bones offer few characters indicating the side of the 
body to which they respectively belong. One (probably the right) is 133" in length, 
