THE ANATOMY OF A HAMMEBHEAD SHARK. 



975 



Another pair of large foramina, one on each side, is seen 

 perforating tlie inferior pre-auditory ridge [i.jj.r.), which runs 

 anteriorly from the auditory capsule. 



Two small apertures (s.o.) ventral to the foramen magnum 

 serve for the passage of the first spino-occipital nerve. 



The posterior view of the skull shows the apertures for the 

 ninth and tenth cranial nerves in the normal position ; the 

 fairly large foramen of the vagus nerve (x) at the sides of 

 the occipital processes, and the small foramen for the glosso- 

 pharyngeal nerve (ix) at the postero -lateral corner of the auditory 

 capsule. 



The posterior portion of the skull seen in lateral view (text- 

 fig. 4) shows a number of foramina. The most posterior of these 

 is that of the vagus nerve (x), and slightly anterior to this is the 

 foi'amen of the glossopharyngeal nerve (ix). 



Text-figure 4. 

 KM op. sp-r. p.f. YMm. 



^ sa.p. 



b.y.--:-h 



P- h.a 

 Lateral View of Posterior portion of Cranium. 



a.s, articular facet for lij^omandibular 



cartila£;e. 

 h.ti. passage for blood-vessel. 

 Ti.a. passage for hj'oidean artery. 

 i.e. interorbital canal. 

 i.^.r. inferior pre-auditory ridge. 



p. articulating process on ventral side 

 of cranium. Seeker inserted to 

 show large foramen. 

 sa.p. supra-auditorj' process. 

 s.f.r. superior pre-auditorj- ridge. 



The posterior seeker marks the 

 foramen perforating the inferior 

 pre-auditory ridge. 

 II-X. Cranial nerves. 



The pre-auditory depression exhibits the following apertures : — 

 the largest, which is situated near the posterior of the depression, 

 is the foramen of the fifth, sixth, and seventh cranial nerves 

 (v, VI, Yii), excepting the ophthalmic branches of the fifth and 

 seventh nerves. Ventral to this are three small apertures, the 

 anterior of which serves for the passage of the hyoidean artery 

 {h.a.). The posterior of the three is the interorbital canal 

 (i.e.). The third aperture, which is situated between and slightly 

 dorsal to the others, is the foramen of the third cranial nerve (lii). 



The large optic foramen (ii) is situated immediately anterior to 

 the foramen of the chief branches of the fifth and seventh and 



