SKELETON 



75 



sixth and the ophthalmic branch of the fifth nerve pass, the rest 

 of the fifth nerve passing through the aUsphenoid bone. The optic 

 nerve usually perforates the orbitosphenoid, but may pass through 

 notch in its margin. 



The ethmoid plate may ossify into a median mesethmoid bone 

 bounded on either side by an ectethmoid and in some there may be 

 added other bones included among the 'turbinal bones.' The ol- 

 factory nerves pass on either side of the mesethmoid, the ectethmoids 

 (below) in the mammals developing as perforated plates (cribifonn 

 plate) . 



ro< 



Fig.' 75. — Dorsal view of schematic skull, the chondrocranium dotted, cartilage 

 bones with lines and dots, pretnax, premaxilla; pref, prefrontal; postfr, postf rental; 

 pastor, postorbital; sguamos, squamosa]; quju, quadratojugal; qu, quadrate; in/>, inter- 

 parietal; exoc, exoccipital; supratem, supra temporal; supraoc, supraoccipital; other 

 names in full. 



A series of otic or petrosal bones is developed in each otic cap- 

 sule. The most constant of these are a prootic in front, an opisthotic 

 behind, the two usually meeting below (fig, 74), and between them, 

 above, an epiotic, concerning which more evidence is needed. In 

 the teleosts and some other forms the lateral wall of the otic capsule 

 may develop, in addition, a sphenotic in front and a pterotic behind, 

 the latter overlying the horizontal semicircular canal of the ear. In 

 the higher groups the various otic bones fuse in the adult to a single 

 petrosal bone, which is wedged in between the lateral parts of the 

 basioccipital and basisphenoid. 



