COMPARATIVE STUDY OF a'OMliEOID FLSUIÜ 317 



small piut ill the Literal wnll of the l>raiii-C!ivitj, genenilly with two concjvvi- 

 ties. In the Tliunnidre the spheuotic luis a large concavity inside, and another 

 large one outside. The latter forms the Ijottom of a deep pit on the ventral 

 surface of the cr.iniuiu. The dorsal surface of the sphenotic, lying between 

 the temp>ral and pterotic crests, is divided into two, by a process of the 

 piriotiil, extending over these Iwues and joining the anterior, internal an'uer 

 of the pteratic. In the Katsuwonidiij the spheuotics are nearly like those of 

 the TluinnidtB ; but they appear oiil^- a little at the dorsjil surface of the 

 cniniuin between the two lateral crests, or they do not appear at all (Auxis). 

 Moreover at their ventral surface, we fiud a depression at the posterior, internal 

 corner. 



The basisphenoid is the smallest cranial bone, Y-slia^jed, median in 

 position, and lies between the prootics and alisphenoids on the craniid iloor. 

 Tlio median vertiad process is laterally compressed, and is united to the 

 parasphenoid, thus divi ding the mouth of the myodome into two. In the 

 Scombridao the medi;in process is very long, naiTow, but in the Cybiida3 and 

 Plecostei it is rather broad. 



The epiotics form the dorsal posterior part of the periotic capsule, lying 

 on both sides of the posterior part of the supraoccipital, and anterior to the 

 esoccipitil. They are joined posteriorly to the exoccipitids with a rather 

 straight suture, externally to the pterotics, and [interiorly with the parietals, 

 iuid sometimes with the sphenotics. In the inner side of the cranial cavity, 

 the epiotics are bounded by the supraoccipital, prootics, and exoccipitals, and 

 sometimes by sphenotics as well. They have each a rough ja-ominent epiotic 

 process to unite with the flat doi-sal process of the posttemixjral. The epiotic 

 process is continuous to the temporal crest; but in Scomber the process and 

 the crest are separate. In the Scombrida3 the epiotics are markedly prominent 

 as the external posterior ridge of these bones is vertical as in the SeiTanid;B 

 and Carangidfe ; but in the Cybiidas and Plecostei the ridge gividually slopes 

 downward and outward. In the Cybiidie a deep groove or a canal is t)ften 

 found in the internal side of the epiotic to receive the anterior semicircular 

 canal of the auditory organ. In Katsuiocmus we find a trianguUr process in 

 tile internal side of the epiotic to separate the dorsal part of the anterior 

 semicircular canal. 



