io8 



VERTEBRATE SKELETON 



median line. The supraoccipital is sometimes excluded from the 

 border of the foramen magnum by the exoccipitals. The exoccipitals, 

 pierced by the ninth and tenth nerves (sometimes by the spinooccip- 

 itals), usually meet below the foramen, excluding the basioccipital 



Fig. 114. — Dorsal and ventral sides of skull of Pleiironectes (Cole and Johnstone, 

 '01); dotted lines show planes of symmetry, as, alisphenoid; bo, basioccipital; c, 

 carotid foramen; cc, cranial cavity; e, ethmoid cartilage; eo, exoccipital; epo, epiotic; 

 j, jugular foramen; //, left frontal; Ipf, left prefrontal; of, olfactory foramen; opo. opis- 

 thotic; p, parietal; pro, prootic; ps, parasphenoid; pto, pterotic; rf, right frontal; rl, 

 right lacrimal; rn, right nasal; rpf, right prefrontal; so, supraoccipital; spo, sphenotic; 

 V, vomer; 5-10 nerve exits. 



from its wall. In Ostariophysise an internal process from each 

 exoccipital forms the floor of the posterior part of the brain cavity, the 

 space below being occupied by the vestibular sacs of the ear, while 

 in Cyprinoids (fig. 115) a foramen in each exoccipital connects the 



