SKELETON OF THE WHALE. 155 



those that have " chevron bones" articulated to their 

 under part. This special name is given to the vertebral 

 elements called " haemapomophyses" (see Fig. 26, h\ 

 which are articulated in cetacea as in crocodilia, directly 

 to the under surface of the centrum, and, coalescing at 

 their opposite ends, develop thence a " hsemal spine," and 

 form a "haemal" canal analogous to, but not homologous 

 with, that in fishes (compare No. V, A, with No. I, ^, in 

 Cut 10, p. 182). The caudal vertebrae of whales further 

 differ from those in fishes in retaining the transverse pro- 

 cesses, and in becoming flattened from above downwards, 

 without coalescing. These modifications relate to the 

 support of a caudal fin, which is extended horizontally 

 instead of vertically. 



Whales and porpoises progress by bounding move- 

 ments or undulations in a vertical plane, and their neces- 

 sity of coming to the surface'to inhale the air directly, as 

 warm-blooded mammals, calls for a modification in the 

 form of the main swimming instrument, such as may best 

 adapt it to effect an easy and rapid ascent of the head. 



The course of the whale is stopped and modified by 

 the action of the pectoral limbs, which are the same 

 parts as those in fishes, but constructed more after the 

 higher vertebrate type. The digital rays do not exceed 

 five in number ; but they consist of many flattened pha- 

 langes, and are enveloped in a common sheath of integu- 

 ment. A radius, 55, and an ulna, 54 (Fig. 25), support 

 the carpal series ; but, instead of being directly articulated 

 to the scapular arch, they are suspended to a humerus, 

 53: this is a short, thick bone, with a rounded head. 

 The scapula, 51, is detached from the occiput, has a short, 

 stunted, coracoid anchylosed to it, and is thus freely sus- 

 pended in the flesh ; it develops an acromial process : the 



