1. supra-occipital. 2. epi-otic. 3. pterotic. 4. opisthotic. 5. exoccipital. 6. basi-occipital. 7. parasphenoid. 8. sphenotic. 9. alisphenoid. 10. orbitosphenoid. 11. lateral- or ectethmoid. 12. olfactory pit; the vomerine teeth are seen just below. 14. pro-otic. 15. basisphenoid. 16. foramen for the passage of an artery. 17. anterior fontanelle. 18. posterior fontanelle. I. II. V. VII. IX. X. foramina for the passage of cranial nerves.] In front of the exoccipital is the large =pro-otic= pierced by two prominent foramina. Through the more dorsal of these (fig. 10, VII.) the facial nerve passes out, while the more ventral (fig. 10, 16) is for the passage of an artery. Dorsal to the exoccipital are the =opisthotic= and =pterotic=, and dorsal to the pro-otic is the =sphenotic=. The =pterotic= is marked by a prominent groove often lined by cartilage, which is continued forwards along a tract of cartilage between the pro-otic and sphenotic. With this groove the hyomandibular articulates. There are considerable ossifications in the sphenoidal region of the side of the cranium. The anterior boundary of the posterior fontanelle is formed by the large =alisphenoid=, which is continuous behind with the pro-otic and sphenotic, and below with a slender =basisphenoid=. Both in front of and behind the basisphenoid there are considerable vacuities in the walls of the cranium; through the posterior of these openings (fig. 10, V.) the main part of the trigeminal nerve passes out, and through the anterior one, the optic (fig. 10, II.). The alisphenoid is continuous in front with the =orbitosphenoid= (fig. 10, 10), which is pierced by the foramen for the exit of the first nerve (fig. 10, I.), and in front of the orbitosphenoid there is a large vacuity. The =lateral ethmoid= is seen in the side view as well as in the dorsal view. Further forwards are seen the olfactory pits, and the long cartilaginous snout. A =ventral view= of the cartilaginous cranium shows much the same points as the side view. The basisphenoid appears on the surface immediately in front of the basi-occipital. THE SKULL WITH MEMBRANE BONES. The =dorsal surface=. The greater part of the dorsal surface in front of the supra-occipital is overlaid by a pair of large rough _frontals_ (figs. 9, A, 5, and 10, 5). They cover the posterior fontanelles and stretch over from the sphenotic to the lateral ethmoid, forming a roof for the orbit. They meet in the middle line behind, but in front are separated by a narrow tract of unossified cartilage, and are overlapped by the _median ethmoid_ (figs. 9, A, 6, and 11, 6). At the sides of the supra-occipital behind the frontals are a pair of small _parietals_ (figs. 9, A, 7, and 11, 7). [Illustration FIG. 11. LATERAL VIEW OF THE SKULL OF A SALMON (_Salmo salar_) (after PARKER). Cartilage is dotted.