below the large foramen just mentioned is a small hole through which the external carotid enters the orbit (fig. 6, 9). [Illustration Fig. 6. LATERAL VIEW OF THE SKULL OF A DOGFISH (_Scyllium canicula_) × 2/3.] 1. nasal capsule. 2. rostrum. 3. interorbital canal. 4. foramen for hyoidean artery. 5. foramen for the exit of the ophthalmic branches of Vth and VIIth nerves. 6. foramen through which the external carotid leaves the orbit. 7. orbitonasal foramen. 8. auditory capsule. 9. foramen through which the external carotid enters the orbit. 10. ethmo-palatine ligament. 11. palato-pterygo-quadrate bar. 12. Meckel's cartilage. 13. hyomandibular. 14. cerato-hyal. 15. pharyngo-branchial. 16. epi-branchial. 17. cerato-branchial. 18. gill filaments, nearly all have been cut off short for the sake of clearness. 19. extra-branchial. 20. pre-spiracular ligament. II. III. IV. V. Va. VIIa. foramina for passage of cranial nerves. Behind the orbit is the =auditory capsule=. This is marked below by a prominent =surface for the articulation of the hyomandibular=, above which is the deep =postorbital groove= for the passage of a blood-vessel, connecting the orbital and anterior cardinal sinuses. (_c_) Passing to the posterior end of the cranium: in the centre is seen the large =foramen magnum= through which the brain and spinal cord communicate. The =notochord= enters the skull just below this foramen, and on each side of the notochord is a projection, the =occipital condyle=, by which the first vertebra articulates with the skull. External to the condyles are the prominent =pneumogastric foramina= for the passage of the tenth nerves, and further to the sides, just beyond the posterior vertical semicircular canals, are a pair of deep pits in which lie the =foramina for the ninth nerves= (fig. 6, IX). (_d_) The broad and flat ventral surface of the cranium is continued in front as the =internasal septum= and terminated laterally by the =suborbital ridges=. At a little behind the middle it is traversed by two shallow grooves along which the internal carotid arteries run. At the divergent ends of these grooves are seen two small apertures through which the external carotids enter the orbit (fig. 6, 9), and at the point where they meet is a single small aperture through which the internal carotid enters the cranium. (2) THE VISCERAL SKELETON. The =Visceral skeleton= forms a series of seven cartilaginous arches or hoops, surrounding the anterior part of the alimentary canal, and enclosing a wide but rather shallow space.