31 KAMAKICHI KISHINOUYE: 



The pterotics are rather thin, more or less elongiited liories, forming the 

 lateral posterior comer of the skull, at the corner the bones are poiuted, and 

 more or less produced posteriorly to form the pterotic process. On the 

 ventral surface the bones liiive a large facette for the articulation of the 

 posterior portion of the hyoiuandilmlar. There is a protuberance or a process 

 in the midway of the external margin. Anterior to the jJrotuberance the bone 

 forms the posterior part of the outer cranial crest. lu the Scorabrid» and 

 Cybiidre the pterotics are flattened and comparatively narrow in the ventral 

 side, but in the Plecostei a special process is j)roduced at the inner anterior 

 coiTjer of the hyomandibular facette, below the ventral groove of the skull. 

 The lateral posterior coi'ner of the pterotics is much produced in tlie Katau- 

 wonidaB ; but the process is not distinct in many forms of the Cybiidir. 



The prootics are seen from the veuti'al side of the skull only. They 

 meet very firmly at the venti'fJ median line of the brain-capsule. They are 

 lx)uuded by all the cranial lx)ues of the brain-capsule, except the i^rietals and 

 the supraoccipital. They are very iiTegular in sha^oc, aud rather large. In 

 these bones "we can distiuguish two lamella?, horizontal aud vertical. Li the 

 ScombridsB and Cybiidas the verticiil lamella is nearly smooth and oblique ; but 

 in the Plecostei the vertical lamella is high, more or less twisted, and is 

 moreover divided into two parts. These two parts meet in a line over the 

 foramen jugulare in the Thnnnida? ; but in the Katsuwonidse they are not two 

 independent processes in diilcnmt planes, and there is no foramen jugulare. 

 These bones form the wall of the medulla oblongata aud also receive the 

 ventral and nearly horizontal part of the auterittr canal of the auditory 

 organ. Generally speaking the bones are more or less flattened exte iorly, 

 luit tliere ai'e two or three deep grooves on the inner side to receive the 

 gi'eater part of the auditory organ. The foramen jugulare hes upon the 

 horizontal bridge. In the Scombridio and CybiidiO the prootics take no part 

 iu the formation of the hyomandibular cup. 



Hie exoccipitals correspond witliout doulit to the neimil spine of the 

 vertebra aud protect the auterior cud of the spiual cord, enclosing the forameu 

 magnum. Each exoccipital lias a lai-ge paraoccipital c<^udyle. The lx)ues may 

 l« seen from the dorsal and ventral sides of the skull. They are bounded by 

 the epiotics, opisthotics, prootic^s, and basioccipital, aud sometimes a little by 



