COMPARATIVE STIDV OF SlOJIBROIl) FLSHlvS. 377 



VGiitral. Those numerous artoriolos uourisLing the dark red p>rtioii of the 

 lakTal muscle run axially. lu Etdhynmts aud A^txts there ai« two pairs of cutaneous 

 arteries originating from two diflereut jxjints. The anterior pair is smaller, 

 homologous to the hypixial hmb of the cufcmeous artery of Katsutoonm, and 

 is given oflf fiom the Ixxly segment of the sixth vertebra. The artery takes a 

 more or Itss forward direction, pisses through the kidney and then turns 

 backwai-ds. The artery has no relation with the dark red muscle. Th»; 

 jxjsterior pu'r is very thick, nearh' jus thick as the dorsal aorta or a Httlc 

 tliickcr thiui it, probably homologous to the whole cutaneous artery of the 

 Thmuiidae. The posterior jxiii- of cutaneous arteries takes an obhquely upward 

 and backward direction, and makes its appearance at the surface of the body, 

 between the intermuscular bones of the fourth and fifth vertebrae. The ai-tery 

 runs a little above the lateral median line, aud seems to vanish in the cjiudal 

 part. Tlie cutaneous artery sends oft' segmental branches to the surface of the 

 body, both dorsal and ventralwards, and axially very numerous arterioles to 

 the dark red portion of the lateral muscle. These arterioles are lUTanged in 

 two diverging sheets to invest the dai-k red j^wrtion of the lateral muscle. In 

 a rare abnormal case, I found the posterior cutaneous artery joined to the anterior 

 cutaneous artery, but in such cases the abnormality is found in one side of the 

 body only. 



In the Plecostei ßuljspinal viiscuLir plexus or the kurochiai, the vascular 

 plexus in the haemal canal, deseiTe attention. In Neothunnus vertical aiierioles 

 originate iis short parallel ninnerous vessels hxym the dorsal aorta in the same 

 way as the accompanying venules originate from the caxxJiual vein aud these 

 together make a black red i-od as thick jus a thiuub. These numerous aiierioles 

 unite again to two pairs of segmental aiieries in each body-s^ment, one along 

 the intt^rmusculai* bone, the other along the neural spine. Tn the Katsuwonidae 

 the sulispinal vascular plexus does not lie just beneath the vertebral coliunu 

 but is more or less sepu'ated finm the latter. In Eiithjnnus aud Auxis 

 (fig. 2) the doi-sal aoi"ta is so remarkably separated from the veiiebral colmnu 

 that tlie kurochiai is lx>nt hke a bow. In Auxis the arteiioles are few in 

 number and the subspinal vtisculai- plexus is much d^;euerated. The obhque 

 segmental aileries from the dorsal aoi-fai nourish the dark red portion of the 

 lateral muscle from the axial side. 



