96 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Delphinapterus leucas, Pall. 



Kiikenthal has shown that this species exhibits another 

 phenomenon in the hand skeleton. This consists in the 

 longitudinal splitting of digit No. 5. The condition shown in 

 Foetus C. is interesting in this connection. This foetus is quite 

 a small one, but the digit No. 5 does not show any signs of the 

 splitting as described by Kiikenthal. Digit No. 4, however, 

 shows a well-marked branch, lying between this digit and digit 

 No. 5. The branch springs from the first phalanx, and itself 

 consists of four well-marked phalanges. 



EXPLANATION OF PLATE 



Fig. 1. Balaenoptera physalus (Linn.). 



Foetus A. Left Pectoral Fin. x 4. 



Fig. 2. Balaenoptera physalus (Linn.). 



Foetus A. Right Pectoral Fin. x 4. 



Fig. 3. Balaenoptera physalus (Linn.). 



Foetus B. Right Pectoral Fin. x 2. 



Fig. 4. Delphinapterus leucas, Pall. 



Foetus C. Right Pectoral fin. x 4. 



I-V = Digits Nos. one to five ; Br. = Branch of Digit 

 No. IV ; pi = pisiform ; pp = prepollex ; r = radius ; 

 u = ulna. 



