I04 



VERTEBRATE SKELETON 



connected with the trabecula. The early chondrocranium of Amia has several 

 peculiarities. The trabeculae are widely separated from the anterior end of the 

 notochord, but meet it further back; they unite in front as a narrow mesethmoid 

 and then diverge as cornua which are joined by the anterior ends of the ptery- 

 goquadrates. The large otic capsules are widely open to the brain cavity. 

 The hyomandibula, perforated for the hyomandibular nerve, is fused with the 

 otic capsule and its lower end is a narrow symplectic process extending towards 

 the angle of the jaw. The sphenolateral cartilage, appearing later, is separated 

 from the trabecula by a wide gap, both cartilages meeting in the nasal capsule 

 which has a fenestrated roof, the capsules of the two sides being separated by a 

 wider ethmoid plate. The cartilage roof of the cranium is added later and is 

 complete, without fontanelles. Three vertebral arches are absorbed in the 

 occipital region. 



Several bones develop in the chondrocranium, none needing 

 detailed description, and Httle more need be said of the membrane 

 bones of Amia, save that the one here called supraethmoid is often 

 called ethmoid, but is membrane in origin. The so-call&d intercalare 



Fig. 112. — Skull of Lepidosleus. cl, clavicle; cor, coronoid; d, dentale; do, dermocci- 

 pital; /, frontal; tor, infraorbitals; mx, maxillary ossicles; n, nasal; op, operculare; or, 

 orbit; p, parietal; pn, prenasal; po, postorbital; pop. preoperculum ; scl, supracleithrum 

 (posttemporal) ; sop, suboperculum; si, supratemporal. 



is probably opistho.tic. The other bones are much Hke those of 

 lower Teleosts, the absence of a supraoccipital separating Amia from 

 most bony fishes. 



Lepidosleus diflfers in several respects from other Teleostomes. 

 Nasal and premaxilla are apparently fused in the tip of the snout, 

 and in front of them is a prenasal on either side. Instead of a 

 single premaxilla there is a series of maxillary ossicles, each bearing 

 teeth. The orbit is surrounded by orbital bones, the preorbitals 

 extending some distance in front of the orbit. The squamosal is 



