COMPARATIVE STUDY OF SCOMBROID FISHES. 
339 
but in Neothwmus it is nearly equal to or broader than the diameter of the 
vertebral column, and it is still wider in Katsuivonus and Eulhynnus (figs. 57, g ; 
58, g). In the Katsuwonidae the canal is separated from the vertebral column 
by the development of a peculiar median process which I propose to name as 
the epihaemal process. These processes as well as the neural, and haemal 
processes are more or less laterally compressed. The neural and haemal processes 
are greatly bent backward near the distal end in vertebrae of the middle 
part of the vertebral column. In Auxis the haemal canal is not closed in the 
precaudal region. In Thunrns and Parathunnns the haemal canal is closed in 
the 10th vertebra ; but in NeotJiunnus in the 11th. In the Katsuwonidae the 
canal is closed still further back :—In Katsuivonus 12th, in Euthynnus 16th, 
and in Auxis 21st. 
In the Thunnidae the first vertebra is very short, and is always anchylosed to 
the occipital region with a zigzag suture, so firmly that many authors overlooked 
its centrum, though they found the detachable neural arch belonging ,to it. The 
anterior margin of the first neural spine is not straight, but notched. In 
the vertebrae of the Thunnidae the longitudinal grooves are conspicuous, 
especially the lateral grooves. The vertebrae are massive, and are fiuely 
striated at the surface, and the internal part is alveolar. The inferior 
foramen as well as the haemal canal are very poorly developed in Thunnus 
and Parathunnus ; but in Neothwmus they are well developed in caudal vertebrae. 
In this family the transverse process is developed from the fourth vertebra. 
It is well developed in the following three to five vertebrae, as a short, nearly 
fiat process with a more or less trenchant edge. In the Katsuwonidae the first 
vertebra differs but little in size from the following vertebrae, and is less 
firmly anchylosed to the skull, and at the same time the relation between its 
centrum and the neural process is much closer, not easily separating from each 
other. The lateral grooves of the vertebrae communicate with each other near 
the axis in anterior vertebrae of the precaudal region, and in Euthynnus and 
Auxis (fig. 15) the ridges between these grooves are poorly developed or 
disappearing, thus the vertebral column is much more slender than in the 
tunnies. The mass of the vertebrae is greatly diminished, as the interior 
alveolar part is nearly lost, leaving the hard, compact, cortical layer only. The 
surface of the vertebrae is nearly smooth. The inferior foramen is enormously 
