20 OSTEOLOGY OP SCOMBROID FISHES 



The basisphenoid is present and has a descending process to the 

 parasphenoid. The alisphenoids are widely separated by the anterior 

 opening to the brain cavity. The prefrontal is elongate and meets its 

 fellow of the opposite side at the median line in front of the orbital 

 cavity. It has the usual lateral wing which is pierced by the olfactory 

 nerve and supports the posterior end of the palatine below. In front 

 of the prefrontal a lateral protuberance is formed by the vomer and 

 ethmoid and extends up nearly to the frontal. The vomer is obliquely 

 truncate on each side for the articulation of the maxillary. The opis- 

 thotic is on the lower surface of the cranium covering the exoccipital- 

 pterotic suture, and scarcely showing on the superior surface. To its 

 posterior edge the lower limb of the post-temporal is attached. 



The nasals are rather wide and are attached to the front of the 

 frontals and ethmoid. They are produced anteriorly in front of the 

 ethmoid over the maxillary. The preorbital is long and carries a sensory 

 tube in continuation with that of the suborbitals. The suborbitals are 

 little more than a chain of small bony tubes, but they form a complete 

 suborbital ring. There is no suborbital shelf, and the eye is not incased 

 in a bony sclerotic cup. 



The premaxillary bears only a slight suggestion of an ascending 

 process. The maxillary carries a long, narrow, supplementary maxillary 

 along its upper edge. The anterior inner end of the maxillary has a 

 conspicuous fascet for articulation with the vomer. The teeth on the 

 side of the premaxillary are set in alveoli, but the long lance-like canines, 

 forming a short inner row in front, though developed from cavities are 

 of a different character, as the cavities behind them become filled with 

 "bone of attachment" as the teeth are pushed out. 



The head of the hyomandibular is divided into two parts, though 

 a little less completely than in the Scombrida?. The opercular elements 

 are not so smoothly united to each other. The upper part of the sym- 

 plectic is united to the metapterygoid by a dentate suture as in Sarda 

 and Thunnus. The palatine is armed with a single row of small sharp 

 teeth, and anteriorly the usual process extends over the maxillary. The 

 articular entirely fills the notch in the dentary; a small angular is pres- 

 ent. The teeth at the side of the dentary resemble those of the pre- 

 maxillary, but one or two teeth at the front are apparently of the 

 character of the inner premaxillary row. 



The posttemporal is a slender, widely forked bone. Its upper 

 limb is rather solidly attached to the epiotic, and slightly overlaps the 

 parietal, but it does not impinge on the supraoccipital as in some of 



