NO. 8 INTERRELATIONSHIPS OF THE CETACEA WINGE I9 



ponderant as regards the body than in other whales. The cervical 

 vertebrse are pressed together unusually strongly ; they coalesce. 



Balcena appears in some respects to stand on a lower level than 

 Ncobalccna. Its slender under jaw seems better to agree with the 

 condition primitive to the cetacea than does the strikingly massive, 

 strongly compressed under jaw of Ncohalcena in which the mandible 

 presumably must be especially influenced by the large under lip. Its 

 relatively few, ordinarily formed, slender ribs, and its correspond- 

 ingly rather long series of lumbar vertebras are also undoubtedly 

 primitive characters ; in Ncohalcena the ribs have become unusually 

 numerous and the number of lumbar vertebrse is reduced to a few 

 bones, while the ribs, or at least most of them, have become remark- 

 ably broad and have to a remarkable degree lost connection with the 

 vertebras so that they lie loose among the muscles. Balcena is no 

 doubt the more primitive also in the short, broad form of the hand. 

 The first finger is either (in B. australis) rather well developed, con- 

 taining two phalanges in addition to the metacarpal, or (in 5. mysti- 

 cetus) reduced, though still retaining the metacarpal." The other 

 fingers are not much lengthened ; in the median digits, however, 

 especially in the third, the number of phalanges may be increased to 

 four or five. The form of the phalanges is terete, not compressed. 

 In Neobalcena, the hand appears to have essentially the same structure 

 as in Balcsna, but the first metacarpal is said to be absent, and the 

 entire hand has become narrower. The lack of a dorsal fin in Balcena, 

 in contrast with Ncohalcena, is, presumably, also a primtive character ; 

 though the fin may have been lost. But in the adaptation of the head 

 as a pouch for catching small animals Balcena has reached far beyond 

 Ncohalcena. In the more primitive of the two certainly known species 

 of Balcena, B. australis, the modification is a little less noticeable than 

 in the higher species, B. mysticetus; the head is slightly smaller, the 

 upper jaw is somewhat less bowed upward, etc. In B. mysticetus the 

 head becomes so huge that in full grown individuals it reaches a 

 third or more of the animal's total length, the upper jaw is thrown 

 upward in an enormous arch, the palatine and pterygoid are forced 

 backward under the hindmost part of the basioccipital, etc. The 

 coracoid process of the scapula may be absent (in B. australis). 



Ncohalcena must assuredly have originated from Balcena, but from 

 one of the most primitive species of the genus, in which the head was 

 only a little increased in size ; but since then it has gone its own way, 

 developing peculiarities in the form of the lower jaw, in the ribs, 

 vertebral column and hand. 



