224 MR. W. K. PARKER ON THE STRUCTURE AND 



the palato-suspensorial arch is rather feeble ; the pre-palatine (fig. 4) is blunt ; the 

 pedicle (pd.) is short, and the quadrate region (fig. 3, q.c.) of the average length ; it is 

 partly ossified. The pedicle glides on a disk, which has a thick rim ; the pait of the 

 pterygoid (pg.) which invests it is at right angles with the main part. The palatine 

 bone (^x(.) is a feebly falciform lamina lying loose under the cartilage ; the condyle for 

 the jaw (q.c.) is large and reniform. 



The "annulus" (figs. 3 and 5, a.ti/.) is one-third less than the average size, and is an 

 oblique, open crescent ; the stapes (st.) is a very regular ellipse, of medium size and 

 slightly calcified. In front of the stapes, and passing a little inside its antero-superior 

 edge, there is another ovoidal cartilage (co.), from the outside of wliich there grows a 

 thick, short spike, also uuossified ; this ends in a fibrous thread which passes over the 

 hind lunb of the annulus and under the facial nerve (VII.). This "columella" is an 

 accurate countei-part of that of the young Toad (fig. U); the inter-stapedial region Ls 

 here, with a rudiment of the medio-stapedial. The stylo-hyal (st.h.) is small above, 

 and only partially confluent ; the cerato-hyal band (fig. G, c.hy.) is narrow and uni- 

 form; the hypo-hyals have a lobe, growing forwards, and are straight and long, 

 bounding the very deej), semi-elliptic notch. The basal plate is long and wide, the 

 anterior and posterior lobes are part of the same expansion, and the front part has a 

 larger outer and a smaller inner projection ; the thyro-hyals (t.hy.) are long, straight, 

 and but little divergent. The Eustachian openings (eii.) are of moderate size and 

 circular. The investing bones are very much like those of the young Toad (figs. 7, 8); 

 the fronto-parietals {f-})-) leave the superoccipital region bare, behind, and do not cover 

 all the fontaneUe, and but liitle of the girdle-bone in front. The nasals («.) are wide 

 apart, they do not overlap much of the nasal region, and cover but little of the 

 roof; they are small sub-crescentic shells. The premaxiUaries (^^.r.) are well under the 

 snout, and are tilted forwards, above; the maxillaries, quadrato-jugals, and squamosals 

 {mx., q.j., sq.) are normal, but feeble; I find no septo-maxillaries ; the parasphenoid 

 and vomers are like those of a young Toad. The mandible (fig. 3) is normal, but 

 rather feeble; the dentary (d.) is more than half the length of the ramus. 



As compared with the " norma," this skull has the following modifications : — 



1. Its general shape is rather triangular than semi -elliptical ; and its prenasal is 

 very large and projects in front, like that of an " Elasmobranch. " 



2. It has only one fontanelle. 



3. Its hind skidl has only one ossification on each side. 



4. The whole nasal region is very generalised and Raiine. 



5. The annulus is small and very open. 



6. The columella is only a cartilagmous rucUment. 



7. The lateral lobes of the basal plate are confluent, and give oft' three spurs on each 

 side. 



8. Tliere are no dentigerous bones. 



9. The investing bones gcnendly are veiT feeble and arrested. 



