DIPNOI 



occipital neural arches, since it is placed between the hypoglossal 

 and the first occipitospinal nerve (Fiirbringer [14 la]). 



The chondrocranium, complete, thick, and without fontanelles 

 in Ceratodus (Fig. 206), is less complete in the Dipneumones, 



Via. 200. 



Ceratodus Forstcri, Krefl't. A, outer view of left half ; H, inner view of right half, a, angular ; 

 l>h, basihyal ; br, fifth branchial arch ; ch, ceratohyal ; c.r, ' cranial ' rib ; d, dentary ; eo, 

 ' exoccipital ' ; 7im, hyoniandibulur ; h.n, hyomandibular nerve ; hr, hypohyal ; Lp, lateral plate ; 

 m.a, median anterior, and m.p, median posterior plate ; n.a, neural arch ; n.a.c, cartilage of 

 neural arch ; n.s, notochordal sheath ; ii.sp, neural spine ; nt, notochord ; o, opercular, and oc, 

 its cartilage ; pa, parasphenoid ; pf, postf rental ; p.p, pterygo-palatine ; p.t, palatine tooth ; 

 pto, pterotic (?) ; and q, its downward process covering the quadrate cartilage, q.c ; s, sub- 

 opercular ; so, suborbital ; up, isplenial ; s.t, splenial tooth ; r.t, vomerine tooth. 



where the trabeculae remain recognisable, and the wall- of the brain- 

 case is to some extent formed by membrane bones above, below, 

 and at the sides (Fig. 209). The cavity of the auditory capsule 

 is widely open to the interior as in Teleostomes. Fenestrated 

 cartilaginous nasal capsules are present ; also separate nasal 

 cartilages, at all events in Ceratodus (Fig. 207). 



