1 MR. W. H. FLOWER ON THE OSTEOLOGY OF 
determined when a complete and satisfactory classification of the entire group can be 
arrived at. The requisite materials for accomplishing this are at present wanting. 
The anatomy of many distinct forms is still but imperfectly known ; and moreover it is 
probable that there are many others existing as yet undiscovered. We know enough, 
however, to arrive at certain general conclusions. ‘The larger natural divisions may be 
indicated with tolerable certainty ; and when the extent and limits of these become 
generally recognized, much will have been done towards clearing the ground for future 
observation. We shall at least be spared from the irrelevant comparisons, between 
objects essentially dissimilar, with which anatomical treatises on the Cetacea are too 
often encumbered. 
Before proceeding further with this part of the subject, I would remark, in passing, that 
several resemblances pointed out above between the skeleton of this Cetacean and 
that of the Sirenia, according singularly with d’Orbigny’s observations upon its external 
form and habits, can scarcely be regarded as evidences of affinity; they only add 
somewhat to the numerous morphological analogies between the members of these 
essentially distinct orders. 
The interval which separates the Whalebone-Whales from all the Whales with teeth, 
in almost every point of their structure, is far greater than can be found between the 
most widely divergent forms of the latter. Hence the division of the Cetacea into 
several primary groups or families, of which the Whalebone-Whales constitute one, and 
are therefore treated as equivalent to some of the minor groups of the Toothed Whales, 
is quite inadmissible. ‘The recognition of two great and distinct groups (suborders) is 
the first requisite to a right appreciation of the classification of the Cetacea. 
The principal distinctive characters of these two groups were defined in a former 
paper *. Increased knowledge of their structure, especially of the Odontoceti, has 
rendered some slight modifications of these characters necessary. They may at present 
stand thus :— 
1. Mysracoceti or BALaNOIDEA. Teeth never functionally developed, but always disap- 
pearing before the close of intra-uterine life. Upper jaw provided with plates of 
baleen, Olfactory organ distinctly developed. External respiratory aperture 
double. Skull symmetrical. Maxilla produced in front of, but not over, the 
orbital process of the frontal. Lachrymal bones small and distinct from the jugal. 
Rami of mandible arched outwards, their anterior ends meeting at an angle, and 
connected by fibrous tissue, without any true symphysis. Sternum composed of a 
single piece, generally broader than long, and connected only with the first pair of | 
ribs. No costo-sternal bones. All the ribs at their upper extremity articulating 
only with the transverse processes of the vertebra; their capitular processes, when 
present, not articulating immediately with the bodies of the vertebre. 
* Proc, Zool. Soc. 1864, p. 388. 
