l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 'J 2 



muscles on the basal part of the occipital. The palatine may push 

 itself wholly back under the base of the occipital, and the muscle 

 attachment may come to lie about on a line with the posterior margin 

 of the occipital condyle. 



In other respects also the known Balsenids have reached particu- 

 larly high. The supraorbital process of the frontal acquires an 

 unusual breadth, no doubt for the special reason that it follows the 

 eye. which, by the widening of the mouth cavity, is pushed out to the 

 side. The supraoccipital becomes very large and strongly slanting 

 forward under the influence of pressure by the water and by the 

 muscles of the neck. The transverse processes of the thoracic verte- 

 bras become widely projecting ; this is especially noticeable as regards 

 the hindmost thoracic vertebrse (where the processes are para- 

 pophyses, while on the anterior vertebrse they are diapophyses). 

 The ribs have a strong tendency to lose the capitulum and to restrict 

 their connection with the sternum. In most of the recent members 

 of the family the capitulum is absent from all the ribs, even the more 

 anterior, although an evident collum is present (it is, however, doubt- 

 ful whether it is really the capitulum that is absent from the hind- 

 most ribs ; more likely the single articular head which appears to be 

 the tuberculum is in reality either the capitulum alone or the capitulum 

 and tuberculum undifl:"erentiated). The sternum is so reduced that 

 it -consists of the manubrium alone. The first finger has a tendency 

 to atrophy. Etc. 



In the section Balaenini are found the most primitive of the family's 

 known genera : Balcrna and Ncobalccna. With them the anterior 

 facial part of the skull has kept relatively much of the form ordi- 

 narily present in mammals. This is especially true of the inter- 

 maxillary and still more of the maxillary, which is quite slender in 

 front and not depressed. Body and tail are rather short, not quite 

 so well fitted for rapid swimming as in the others. The hand is more 

 primitive. Of the hind limb's skeleton there are present, at least in 

 BaJivna, relatively quite considerable remnants, among other parts a 

 stunted femur and the upper end of the tibia. The mouth is shaped 

 somewhat dififerently than in the others ; it is formed as an enormous 

 barrel or bag, bowed outward on all sides. Not only are the rami of 

 the lower jaw bent outward, but the upper jaw with the whole facial 

 part of the skull is also bent, arched highly upward. Both the upper 

 jaw and the branches of the lower jaw assume the structure of stays 

 in the walls of the pouch-like mouth cavity. The whale-bone plates 

 acquire a remarkable length. I""inally the head becomes more pre- 



