546 MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 
divided longitudinally by the narrow groove representing the neural canal, and cut, 
as it were, in two in the opposite direction by a wider groove connecting the two 
lateral, vertical, vascular canals. Of these four tuberosities, the anterior are larger 
than the posterior pair. In the first vertebra of the series now being described, the 
longitudinal groove is bridged over by a narrow bar of bone, and the anterior and pos- 
terior tuberosities of each side are confluent, but having a canal running under them 
connecting the vascular canals. In the second there is no connexion across the middle 
line; but the anterior and posterior tuberosities unite across the groove on the right 
side. 
The under surfaces also present four tuberosities in the corresponding situation, but 
placed slightly further from the middle line, and showing less dissimilarity in size 
between the anterior and posterior pair. ‘They very much resemble in form and situa- 
tion the processes which bear the hemapophyses in the anterior caudal vertebre. 
The lower openings for the vascular canals, which in the first vertebra of this group 
are placed so near as not to allow of an interval of more than }” between them, in the 
next are 2" apart, and then gradually become somewhat more distant proportionally 
to the size of the vertebre. As their upper ends remain in the same position, the 
canals, from being quite vertical, gradually acquire an upward and inward direction. 
Along the middle of the lateral surface of all these vertebree is a strongly marked longi- 
tudinal grooye, bounded above and below by large rough tuberosities, of which the 
upper one is rather the more prominent, especially at its anterior corner. ‘This peculiar 
form of the side is one of the most characteristic features of these vertebra, and begins 
suddenly in the first of this group. 
It now only remains to speak of the special peculiarities of the last four caudal ver- 
tebre. If we take any one of these, say the third from the end (the twenty-second 
caudal), we shall find that it consists of much more than a simple centrum, the part 
which often is alone represented in this region; but to recognize in it any of the 
ordinary elements of a typical vertebra is by no means easy. We can, however, 
trace a gradual modification from those last described to the one which terminates 
the whole series. Excluding for the present this last named, the other three dimi- 
nish rapidly in breadth, though but slightly in length. The anterior and posterior 
surfaces, to which the intervertebral substance is attached, are deeply hollowed. All 
the processes gradually subside, with the exception of the anterior part of the upper 
lateral tuberosity, which obtains an increased development, forming a distinct process, 
projecting upwards and forwards, from the anterior upper angle of the bone. The 
vertical canals continue ; but their lower openings (which were already somewhat further 
apart in the hinder vertebre of the last group), have, as it were, cut their way out of 
the bone, and form deep grooves on the sides, before perforating the upper lateral pro- 
cess, much in the same manner as in those vertebra where these holes first made their 
appearance. The penultimate vertebra is so much elongated, and constricted in the 
