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the posterior portion of the dorso-mesial edge of the medullary Prolongation; and the posterior portion 

 of the ventral edge of the spina occipitalis is wedged in between the ends of the processes of opposite 

 sides. Anterior to these process-like portions of the exoccipitals the ventral edge of the spina occipit- 

 alis rests on the external surface of the suturating edges of the exoccipitals. In the hind edge of the 

 medullary Prolongation of the exoccipital, there is a large semicircular notch, but it is closed with 

 fibrous tissue and does not give passage to any structure. 



From the internal surface of that part of the exoccipital that lies immediately dorsal to the 

 saccular groove, a stout plate-like process projects mesially and slightly downward, and expanding 

 slightly at its mesial end is in synchondrosis, in the middle line of the head, both with its fellow of 

 the opposite side and with the dorsal edge of that thin median ridge of the basioccipital that separates 

 the saccular grooves; a renmant of cartilage intervening between the three bones. The process forms 

 the roof of a considerable portion of the saccular recess, but does not roof any portion of the cavum 

 sinus imparis, as Sagemehl says that it does in the Characinidae and Cyprinidae, the hind edge of 

 the process only reaching to the anterior edge of that pit. Immediately dorsal to the base, or line 

 of origin, of this mesial process, the exoccipital is perforated by two foramina, one of which lies near 

 the anterior edge of the process, and the other near its posterior edge. The anterior foramen opens 

 on the lateral surface of the bone and transmits the nervus vagus, the other opening on the base 

 of the cond3dar process of the bone, being sometimes double, and transmitting the occipital nerves. 

 Slighty anterior to the vagus foramen the bone is perforated by the glossopharyngeus foramen. 

 On the internal surface of the bone, immediately dorso-anterior to the vagus foramen, there is 

 a recess which lodges the ampulla of the posterior semicircular canal. From this recess two canals 

 Start, one running upward and enclosing a portion of the membranous posterior semicircular canal, 

 while the other runs latero-anteriorly and encloses part of the external canal. The canal for the 

 external semicircular canal lies antero-internal to the angular edge between the lateral and 

 posterior surfaces of the bone, the canal for the posterior canal lying in the ridge that forms 

 a ventral Prolongation of the epiotic ridge. 



The exoccipital is bounded ventrally by the basioccipital, anteriorly by the proötic, dorso- 

 laterally by the pterotic, and dorsally by the epiotic and supraoccipital, from all of which bones 

 it is largely separated by lines of cartilage. The opisthotic overlaps externally the dorsal portion 

 of the lateral surface of the bone, fitting into a depressed region on that surface. 



OPISTHOTIC. 



The opisthotic (intercalar) is a small plate-like bone, quite unquestionably of purely ectosteal 

 origin, which forms the middle portion of the postero- lateral edge of the skull; there .overlapping 

 externally the adjoining edges of the pterotic and exoccipital, and extending forward to, or even 

 slightly overlapping the hind edge of the proötic. Its hind edge is thickened and projects backward 

 beyond the pterotic and exoccipital, there forming part of the lateral wall of the temporal fossa. 

 A small eminence on this edge gives support, and is bound by ligamentous tissue to the ventral end 

 of the opisthotic process of the suprascapular. 



EPIOTIC. 



The epiotic (exoccipitale) is a somewhat pyramidal bone which caps the dorso-mesial corner 

 of the hind end of the temporal fossa and has dorsal, posterior, lateral and cerebral surfaces. A portion 



