COMPARATIVE STUDY OF SCOMBROID FISHES. 
409 
Foramen between tlie basioccipital and parasphenoid is small and opens nearly 
in a horizontal plane. Paroccipital condyles touch each other at the median 
line, and the occipital condyle is only slightly concave. Number of vertebrae 
is 31-64, generally more than forty, and varies greatly even among closely 
allied species. Relative number of the caudal and precaudal vertebrae is also 
variable. Differentiation of vertebrae is a little more advanced than in the 
Scombridae. Sometimes I found abnormal cases in which two or more 
vertebrae fused together. Longitudinal grojves in vertebrae are deep, and 
thus the cross-section of most vertebrae show a six-radiating figure (figs. 
8-12). In some posterior precaudal vertebrae a short haemal process is formel. 
Neural process is broad in some anterior precaudal vertebrae, and the process 
of the first vertebra is free from the centrum. The last caudal vertebra is 
consolidated with the hypural bones, and forms a fan-shaped bone with a 
notch at the median posterior corner. Hypural spine very prominent, but 
rather small in Sarcla and Gymnosarda. One or two auxiliary intermuscular 
bones are found in the occipital region, where the clavicular ligament is 
inserted. Intermuscular bones are weakly developed at the anterior portion of 
the body only, connected by a few and poor tendons. 
Gill-rakers are very poorly developed in the Oybiidae. They are short, 
not much compressed, generally a little more than ten in number, and entirely 
absent in Acanthocybiurn. A few gill-rakers are found near the angle of the 
second branchial arch in some forms. Two or more rows of short denticles are 
found on the inner side of gill-rakers. Ribs are found on the dorsal wall of 
the body-cavity, as myotomes are bent with acute angles. Pelvic girdle narrow 
and elongated. Generally the lower piece of the poslclavicle is nearly straight. 
The vascular system of the Oybiidae has many characteristics :—develop¬ 
ment of the renal portal system from dorsal segmental veins in the precaud¬ 
al region, origination of the genital artery from the dorsal aorta, remarkable 
separation of the dorsal aorta from the cardinal vein with the intervention 
of rete mirabilis of the renal portal system between them. Ureters of both sides 
are entirely separated. Kidneys elongated. Muscles nearly colourless, but the 
median superficial lateral portion is reddish. This reddish portion becomes 
rather thick posteriorly (fig. 17). 
The posterior side of the preopercle is generally a little concave in Gybium 
