110 • MR. W. H. FLO WEE 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 frbm 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. Mystacoceti or Bal^koidea. Teeth never functionally developed, but always disap- 

 pearing before the close of mtra-uterme life. Upper jaw provided with plates of 

 baleen. Olfactory organ distmctly developed. External respu-atory aperture 

 double. Skull symmetrical. MaxiUa 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 pah- of 

 ribs. No costo-sternal bones. All the ribs at their upper extremity articulating 

 only with the transverse processes of the vertebrae ; their capitular .processes, when 

 present, not articulating immediately with the bodies of the vertebrse. 



* Proc. Zool. Soc. 1864, p. 388. 



