CÜMI'ARATIVE STUDY iif.SCOMBROID FISHES. 429 



Portitiüs of the lateiiJ muscle sniToiindod by these sheets of tlio v:iseular 

 plexus are situatetl on biith sides of the vertebnil column, and are dark red, 

 nearly black in colour. Another peculiar vascular plexus is developed f)n the 

 iuner side of the li\<>r ov iu the haemal canal. Moreover the circulation of 

 blood in the liver is especially well developed. 



Thus this gi"oup of fish is distinctly defined from the other forius of the 

 Teleostomi, and comprises the most highly specialized forius of fishes. There 

 is no doubt that they are descendants from the Acanthoptei-ygii, among which 

 they should have been classified. They are most closely alUcd to the geneva 

 Sard" and Gymnosarda of the Cybiidae. 



The bod}- is well adapted for swift locomotion, being plump, ^winted at 

 both ends, and smooth at the sm'face. Caudal peduncle very slender, but with 

 broad Literal keels. Head triangular, nearly flat at the toji. Snout shorter 

 and the mouth smaller thnu iu the Cybiidae, the upper jaw scareeh- reaching.; 

 the vei-tical ft-om the middle of the eye. The pstericn* part of the external 

 mai^in of the upper jaw is not sti-aight, but lx)iit di)wnward, due to the over- 

 lapping of the maxillary over the premaxillaiy. Posterior end of the upiier jaw 

 is stiuight, due to the form of the supplementary bone. Tlie anterior n(;stril is a 

 mere point, and the posteiior ncstiil a trausveise slit. Scales large and thick 

 in the coi-selet, and those behind the eyes are thick and elongated. Scales are 

 ctenoid at the margin but smooth at the surface. Opercular region is entirely 

 nnked. Coiselet is covered with a thick membrane of stixjng connective tissue, 

 to protect the thick part of the peculiar cutaneous vascular system. 



Fins are well developed with tliiek spines and strong fin-rays. In the 

 first doi-sal the fii-st spine is not iuferior in size and thickness to any succeed- 

 ing spiues, and the posterior side of the dorsal outline of the fin is concave. 

 TTie caudal fin is firm and very widely forked, more or less lunate in shajie. 



Gill-rakers ai-e long and fine, and are developed on both sides of bi-anchial 

 arches. Abdominal cavity is narrow and depressed, as the ventral processes of 

 the pi-ecaudal veiiebrae are well developed, consequently the hypaxial jwiiiou 

 of the hiteral muscle iu the pi-ecaudal portion is very tliick (Figs. 18, 19). 

 Portions of the latei'al muscle on both sides of the veiiebral column ai-e 

 coloured dark red or blackish. These jwrtions are called " chiai " in Japanese, 

 and each dark i"ed jxirtion is thick at the anterior end, ta^xiring graduaUy 



