DEVELOPMENT OP THE SKULL IN THE UEODELES. 199 



These fore- and out-growing horns of cartilage- — the "sphenotic" angles (sp.o) — are 

 here nearly as largely developed as in Siren lacertina (Pis. XXXVIII., XXXIX.) ; 

 they do not take the ossifying matter, but remain soft in front of the prootic bones [pr.o). 

 The same thing occurs in the "Anura," but lower down in those types, where the 

 shortened pedicle articulates with similar tracts ("basipterygoids"). 



From the cartilages of the occipital condyles, to the " horn " in front, the whole 

 occipito-auditory tract is ossified above (fig. 2, e.o, pr.o) ; but below (fig. 3) only a 

 crescentic tract of bone clasps the prootic and opisthotic regions ; all the main part 

 of the floor of the vestibule (vb), the stapes itself (st), and a narrowish tract of the 

 tegmen tympani (t. ty) is unossified. 



But up to the antero-internal edge of the fenestra ovalis the capsule has in all this 

 part a second floor of cartilage from the wings of the investing mass {iv). 



The stapes {st) is a large, oval plate, nearly half as large as the unossified vestibular 

 floor ; its direction is outwards and a little forwards ; and the crescentic bony tract 

 which reaches its fenestra behind is the homologue of that bar of the opisthotic 

 which in the Sauropsida and Mammalia divides the fenestra ovalis from the fenestra 

 rotunda. 



The superoccipital " tegmen " only stretches forwards to the middle of the auditory 

 capsules ; they, however, have a narrow selvedge of cartilage which runs forwards into 

 the alisplienoidal wall (fr). The upper fontanelle runs from this part of the roof 

 to the internasal tract ; it is a long oval, pinched in somewhat in the postorbital 

 region. 



In the whole of the orbital region the inner skull is devoid of both roof and floor. Its 

 sides are crescentic in section ; for they grow inwards somewhat both above and below. 

 From the ascending process of the suspensorium [ct.p) to the anteorbital cartilage (e.pa) 

 the w;ill on each side is ossified ; these bones are the sphenethmoids (sjj.e) ; they 

 enclose an oblong skull-cavity, with only gently bulging sides ; the optic nerves 

 (see fig. 7, ii) escape near the end of the wall-bones. 



The internasal cartilage (i.n. c) is a flat plate with the outline of an hourglass, and it 

 reaches halfway to the front margin of the face. 



The large flabelliform cornua trabeculse {c. tr) which it binds together, enclose by 

 their inner projections three fourths of a circle, bounded behind by the internasal band. 

 The angles of these dilated cornua are rounded ; the edge reaches from the palatine 

 plate of the premaxillary to the internal nostril (/. n), a large, oval, oblique passage 

 between the vomers and palatine on the inside, and the unossified membrane in the 

 maxillary region on the outside (fig. 3). 



Above (fig. 2, na), the nasal roofs are crescentic shells of cartilage, with their pointed 

 horns looking forwards and inwards ; the narrow nasal bones (w) only cover their 

 inner horn. 



Behind these cartilages, on the lower plane, the ear-shaped eth mo-palatines {e.pa) are 



