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KAMAKICHI KISHINOUYE : 
The pterotics are rather thin, more or less elongated bones, forming the 
lateral posterior corner of the skull, at the corner the bones are pointed, and 
more or less produced posteriorly to form the pterotic process. On the 
ventral surface the bones have a large facette for the articulation of the 
posterior portion of the hyomandibular. There is a protuberance or a process 
in the midway of the external margin. Anterior to the protuberance the bone 
forms the posterior part of the outer cranial crest. In the Scombridæ and 
Cybiidæ the pterotics are flattened and comparatively narrow in the ventral 
side, but in the Plecostei a special process is produced at the inner anterior 
corner of the hyomandibular facette, below the ventral groove of the skull. 
The lateral posterior corner of the pterotics is much produced in the Katsu- 
wonidæ ; but the process is not distinct in many forms of the Cybiidæ. 
The prootics are seen from the ventral side of the skull only. They 
meet very firmly at the ventral median line of the brain-capsule. They are 
bounded by all the cranial bones of the brain-capsule, except the pari étais and 
the supraoccipital. They are very irregular in shape, and rather large. In 
these bones we can distinguish two lamellæ, horizontal and vertical. In the 
Scombridæ and Cybiidæ the vertical 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 Thunnidæ ; but in the Katsuwonidæ they are not two 
independent processes in different planes, and there is no foramen jugulare. 
These bones form the wall of the medulla oblongata and also receive the 
ventral and nearly horizontal part of the anterior canal of the auditory 
organ. Generally speaking the bones are more or less flattened exteiiorly, 
but there are two or three deep grooves on the inner side to receive the 
greater part of the auditory organ. The foramen jugulare lies upon the 
horizontal bridge. In the Scombridæ and Cybiidæ the prootics take no part 
in the formation of the hyomandibular cup. 
Tlie exoccipitals correspond without doubt to the neural spine of the 
vertebra and protect the anterior end of the spinal cord, enclosing the foramen 
magnum. Each exoccipital has a large paraoccipital condyle. The bones may 
be seen from the dorsal and ventral sides of the skull. They are bouuded by 
the epiotics, opisthotics, prootics, and basioccipital, and sometimes a little by 
