110 



BALJENOrXERID-E. 



from the loose way in which these bones have been counted from 

 defective or badly articulated skeletons ; but, in fact, subject to the 

 exceptional circumstances about to be mentioned, they are quite as 

 constant among the Cetacea as among other Mammalia, and arc 

 therefore characters of the highest importance in determining species. 

 Eveiy example of Balamoptera rosfrata that I have examined in 

 museums, or found recorded, has eleven pairs of ribs, and a total 

 number of vertebrae amounting to 48 or 50. In like manner skele- 

 tons of Physalus antiquorum, Avhen complete, appear always to have 

 15 pairs of ribs and 61 or 62 vertebrae ; Megaptera longimana has 

 14 pairs of ribs and 53 vertebrae ; Balcena Mysticetus 12-13 pairs of 

 ribs and 54 vertebrae. It frequently happens that the last pair of 

 ribs only attain a rudimentary condition, and, their heads not arti- 

 culating with the vertebrae, they are lost in preparing the skeleton. 

 This condition of the last (15th) pair of ribs is well seen in the ske- 

 leton of Physalus antiquorum in the Alexandra Park, prepared by 

 Mr. Gerrard, jun. ; they measure, the one 19|" in length, the other 

 27", and taper to a point at their upper extremit)', being suspended 

 in the position they originally occupied, far removed from the ver- 

 tebral column. A small rudimentary additional rib, or pair of ribs, 

 attached to the first lumbar vertebra, is sometimes developed ; but a 

 fully formed pair of ribs above the normal number is, I believe, never 

 met with. 



Fiff. 12. 



Sternal bones of Fin-Whales of different genera, ^^i\\ nat. size. 



a. Pltysalun antiquonim. Alexandra Park. 



h. Sihbdldiits Svhleyelii. Mns. Leyden. 



c. Bulcenoiptvra rostrata. Mus. Hoy. (^oll. Surg. 



Flower. P. Z. S. 1864, 393. 



