338 KiMAKICHI lOSniNOXJYE: 



together so firmly that the vertebral coliunn allows little motion to eithei" side. 

 The free later.ol motion of the vertebral column is possible only at the root of 

 the caudal fin, where two vertebrae (the last but one and its antecedent) are 

 remaa'kal)ly thin, and their neiu-al and haemal spines are long, diverging, and 

 flattened at the root. GeneiYiUy the number of the precaudal vertebrae is nearly 

 equal to that of the caudal. The vei-tebrae are 18 + 21 in the Thunnidae, 20 

 + 21 in the genus Katsmvonns, and in the other genera of the Katsuwonidae 

 20 + 19. The relative number of the precaudal and caudal vertebrae is often mis- 

 taken, as the haemal spine is also vei-y well developed in the precaudal vei-tebrae. 

 Moreover, it is remarkable that the haemal spine of some anterior precaudal 

 vertebrae is turned forward in the Thunnidae (figs. 49-52, 64). In Aiixis the 

 epihaemal spine is also turned forward in the caudal region too. Thus 

 Katsuivonus has the same number of caudal vertebrae as the Thunnidae, and 

 the numljor of the precaudal vertebrae does not differ from that of the other 

 genera of the Katsuwonidae. In Günther's catalogue less numbei's of vertebrae 

 are recorded ; but this I am inclined to beUeve to be erroneous. Vertebrae 

 differ greatly in shape and structure in the different parts of the body. They 

 are much modified near both extremities of the body; but they ai"e com- 

 paratively simple and hght at the middle. It is noteworthy that the haemal 

 spine is very well developed in some precaudal vei'tebrae too, so that when 

 ribs are detached it is rather difficult to distinguish them from caudal vei-tebrae. 

 However the haemal spine of the precaudal vertebrae is broad, thin and laterally 

 c impressed at the distal end, for the attachment of ribs, and it is of course 

 shorter than that of the anterior caudiil vertebrae. It must be noticed also 

 that the haemal spine of some anterior precaudal vertebrae is turned forward 

 (figs. 49-52). Each vertebra has a pair of short pointed lateral apophyses at 

 the anterior margin of the insertion of the intermuscular bone, especially well 

 developed in the caudal vertebrae. These apophyses serve to keep the inter- 

 musculars fast to the vertebrae. The foiur pairs of zygapophj-ses are well 

 developed, of which the superior prezygapophyses are best developed. In the 

 Thunnidae the transverse process is well developal in some precaudal vertebra« 

 (figs. 13, 49-52, 64). On the dorsal surface of these transverse processes, the 

 head of the intermuscular bones and ribs are inserted close together, the former 

 preceding the latter. The haemal canal is narrow in Thunnus and Paralhunnus ; 



