326 MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 
ceans. The bone is very thick at the sides, where the thyrohyals are attached, but 
becomes gradually thinner towards the posterior (slightly emarginated) border. 
The thyrohyals are somewhat triangular, with a thick, rounded, anterior and outer 
edge, and much thinner behind. The greatest length of each of these is 21", and the 
ereatest breadth 12". 
The basi- and thyrohyals of the Yorkshire Cachalot, which alone are preserved, 
only differ from those of the Tasmanian skeleton in their superior size. The basihyal 
is 182” long by 202” broad; each thyrohyal is 26” long by 14” broad. 
In the breadth and flatness of these bones, Kogia alone (as ascertained from a cast 
kindly sent to me by Mr. Krefft, of Sydney) resembles Physeter. In the Hyperoodon the 
thyrohyals are broader posteriorly than in Dolphins generally, and, so far, present an 
approximation to those of the Cachalot; but, on the other hand, the stylohyals are of 
quite a different form. The absence of union between the basi- and thyrohyals in an 
animal showing all other signs of maturity,.as the Yorkshire Cachalot, is a very peculiar 
feature among Cetaceans. 
Vertebral Column. 
The vertebre of the Cachalot, especially as contrasted with the large Whalebone- 
Whales, present generally a rough or, rather, rugged surface, and a coarse and some- 
what spongy texture. In all the bones, in fact, there is a tendency to the development 
of rough, tuberous and spiculated outgrowths from the surface, and also to irregular epi- 
physial ossifications in the cartilaginous portions of the bone, which afterwards become 
ankylosed, as around the carpal bones, and on the articular surfaces for the chevron 
bones on the lower surfaces of the bodies of the caudal vertebre. The advancing 
ossifying surfaces have generally a much more spiculated character than in other Ce- 
taceans, being covered with pointed conical eminences, which surround the channels 
for blood-vessels. ‘This is also particularly well exemplified in the partially ossified 
carpal bones (see Pl. LXI. fig. 4). The ossification of the ends of the vertebral bodies 
presents a common character by which they can be distinguished from those of all other 
Cetaceans with which I am acquainted. When the epiphysis is removed, rather above 
the centre of the surface (in the dorsal region) is a depressed circular patch, in dia- 
meter rather less than one-third of that of the vertebra; in this part the bone has a 
nodulated appearance,—rather conspicuous pointed tubercles, projecting directly out- 
wards, being scattered over it without definite arrangement (see woodcuts, figs. 5 & 10). 
Outside of this patch, the more elevated surface is roughened by furrows and inter- 
mediate ridges of various lengths and sizes, but all arranged in a tolerably regular 
manner, radiating towards the circumference of the bone. The epiphyses of course 
correspond to this surface, being thickest in the central part. On their outer side, or 
that connected with the intervertebral substance, the limits of this thickened area are 
distinctly seen in the smoother character of the surface, which towards the margin is 
