DEVELOPMENT OP THE SKULL IN THE BATRACHIA. 177 



pital ; the cartilage above them is ossified by the quadrato-jugal {q., q.j.). The annulus 

 (ci.tjj.) is large, broad, and open above; the stapes (fig. 9, st.) is thick and obUque ; 

 the medio-stapedial (m.st.) is a strong, arched rod, having a large ovoidal mass of 

 cartilage on its upper fork, which, however, is not distinct as in the Itust kind. The 

 extra-stapedial (est.) is tongue-shaped ; it has a free rounded selvedge, but no 

 supra-stapedial band. The stylo-hyal (fig. 7, st.h.) is confluent above ; it is very 

 narrow, and widens very little in the cerato-hyal region (fig. 8, c.hy), which is a very 

 narrow tape all through, with only a slight hypo-hyal lobe. The basal plate {b.h.hr.) 

 is largely converted uito the membrane of the great front notch, which is more than 

 twice the extent of the solid tract. 



The narrow ear-shaped front lobes run far along by tlie hypo-hyal, and the hind 

 lobes are small spikes ; in each of these, at their origin, there is an endosteal patch. 

 The thyro-hyals {t.hy.) diverge moderately, are of the average strength, and are 

 sigmoid in form ; they spread well into the basal plate, proximally, and have a blunt 

 unossified end. 



The mandibles (fig. 8) are extremely long and slender ; the dentary {d.) is only one- 

 tliird as long as the ramvis ; the coronoid process of the articulare {ar.) is well formed, 

 and the cylindroidal condyle {ar.c.) is very large; the mento-Meckelian (m.mk.) is 

 small. 



The fronto-parietals (fig. 6, f.j^-) are falcate, less than a tliird the width of the 

 narrowest part of the skull, pointed at both ends, and dilated a little behind, but far 

 apart there; they just touch the ethmoidal wings in front. The nasals (n.) are long, 

 naiTOW; angulate bones, with a small posterior and two large external emarginations. 



The marginal bones {px., mx., q.j., sq.) are all normal and well developed, but are 

 tliin ; there is a good supratemporal plate and post-orbital spur to the squamosal ; 

 there is no septo-maxillary. The parasphenoid ( pa.s.) is large, long, attenuated in front, 

 gnawed externally, and triangular behind. The vomers (r.) are peculiar; the front 

 part is a dilated lobe, giving ofi" a short spike in front of the inner nostril ; then the 

 bone runs along, flat and thin, by the inner margin of that passage up to the ethxno- 

 palatine. This thin part is flanked with a thick, arcuate, dentigerous crest, and the 

 right and left crests running towards each other in front, meet within a distance of 

 one-third then- own length. 



This large Neotropical Tree-frog has an intensely specialised skull, which, however, 

 lies along a line diverging far from that of the typical skuU : — 



1 . The whole skull is extremely depressed. 



2. The ethmo-nasal region takes up half the length of the skuU. 



3. There is only one fontanelle which is totally uncovered by the roof- bones. 



4. All but the small tracts below, and externally, and the fore end of the nasal 

 region is one continuous bony box. 



5. The snout is without a rostnam (normal), but is very transverse, and the roof- 

 cartUages are rather scant. 



MDCCCLXXXI. 2 A 



