MR. W. H. FLOWER ON THE OSTEOLOGY OF THE SPERM-WHALE. 329 
Inia, Pontoporia, Beluga, and Monodon* all are separate, as in the Balenopteride. In 
the other Delphinoids the atlas, axis, and generally one or more of the other vertebre 
are confluent; if any are free, it is at the hinder end of the series. 
The form of the atlas of the Cachalot is very characteristic. The great vertical depth 
of the obliquely truncated transverse processes, and the comparative straightness of the 
upper and lower border, especially the former, give it, when seen either from before 
or behind, a transversely extended quadrangular figure, quite unlike that of any other 
Cetacean atlas. It of course partakes of the regional character of great antero-posterior 
compression, though not to the same extent as the succeeding vertebra. The whole 
bone, with all its inequalities, will lie between two planes 8” apart; and nowhere does 
the actual thickness exceed 6”. The anterior surface is hollowed out to a depth of 43" 
for the reception of the condyles of the occiput. The posterior surface is remarkable 
for its flatness. 
Fig. 2. 
Anterior surface of atlas?+. 
The form of the neural canal, where it pierces the atlas, is very nearly that of an 
equilateral triangle, with one of the angles directed downwards. The upper side is 
almost straight, the outer angles rounded: the lateral sides converge rather rapidly to 
a point rather below the middle, where their posterior margins form an angular pro- 
jection, causing a constriction of the opening. Below this the sides approach more 
gradually towards the inferior angle, which is truncated at the apex. If the anterior 
margin of the aperture alone could be seen, it would appear more perfectly triangular, 
with straight sides. Seen from behind, the opening appears divided by the above- 
mentioned projection on the posterior margin into two parts, an upper transversely 
elongated oval portion, and an inferior narrow vertically elongated part. The former 
alone corresponds to the neural canal of the succeeding vertebre ; the latter fits over the 
rough surface of the axis to which the odontoid ligaments are attached, and affords a 
passage for them. 
* In two skeletons of male Narwhals in the Mus. Roy. Coll. Surg. the bodies of the 2nd and 3rd cervical 
vertebre are firmly united. 
+ The woodcuts of the vertebre (as the figures in Plates LVIII. and LIX.) are all reduced to +4; the size of 
nature. The anterior surfaces are represented in every case. 
