DEVELOPMENT OF THE SKULL IN THE BATRACHTA. 241 



The roof runs on for a third the length of the cranial cavity, but it has two lesser 

 fontanelles (fig. 7) in it ; the main fontanelle is very large and heart-shaped, the 

 front and side growths of the tegmen cranii being slight. The generalised occipito- 

 auditory bones leave the very limited and rounded tegraen tympani {t.ty.) soft ; in 

 front, the bony matter forms a good margin in front of the foramen ovale (fig. 8, V.). 

 Then more than half of the orbital walls are cai'tilaginous (o.s.), and in the middle of 

 each space is the rather small optic fenestra (II.). 



The girdle-bone (fig. 8) is in rudiments right and left, and there is no mesethmoidal 

 bone. Each bony tract is composed of a large cochleate cranial part, separated by half 

 its width from its fellow, and perforated by the orblto-nasal nerve. To this part there 

 is a handle groAvuig out at more than a right angle, and ending in an adze-shaped 

 dilatation (fig. 8, pa.). 



The fact is that the aiTest of the bone towards the middle — above and below — is 

 accompanied with an overgrowth beyond the proper alae of this region, and the whole 

 palatine tract, which has no ectostosis of its own, has become ossified from the ecto- 

 ethmoidal, so that its three regions, ethmo-, pre-, and post-Tpalaiine, are all used up to 

 form the handle to this curious "lateral ethmoid." The well-developed roof and floor 

 of the nasal region (figs. 7 and 8) are entu'ely unossified ; there is a short prenasal (^^•'».), 

 the nostrils (e.n.) are almost tubnlar, and are defended by the normal valves (ti.l^.u.l-.). 

 Below-, the internal nostrils {i.n.) are very wide apart, because of the breadth of the sub- 

 nasal laminae (fig. 8); these end in broad ear-shaped angles, outside, and near the 

 middle have small apiculate pro-rhinals (p.rh.). 



The pterygo-quadrate region is feeble, and the well-shaped, and distinctly -jointed 

 pedicles {pd.), are a lorg distance apart. The pterygoid-bone {pg.) has not ossified 

 aU the cartilaginous band (fig. 7) ; its forks are very short. The quadrate is partly 

 ossified by the quadrato-jugal, and the condyles {q.c.) are oblique, and well-formed, 

 with the hinder lobe of the trochlea much the larger. The Eustachian passage {eu.) 

 is oval, and half the normal size. The annulus (fig. 11, a.ty.) is normal ; its horns do 

 not meet. 



The stapes (figs. 7, 8, 11, and llo, st.) is, relatively, the largest known to me, and it is 

 also the hoUowest, being like an oval Limpet-shell ; on its top is an oblong boss, and its 

 substance is sub-osseous, except in front for a small space : the calcification is passing 

 into true ossification over most of it. The columella is in one piece ; a considerable 

 cartilaginous lobe passes within the stapes, and then it forms an arched rod, the medio- 

 stapedial [m.st); the extra-stapedial [e.st.) is peltate, and has a small rudiment of the 

 supra-stapedial band. The lower hyoid bar has not quite lost its larval solidity ; the 

 stylo-hyal end (fig. 8, st.h.), is massive, and is only partially confluent above. The 

 rest of the bar (fig. 10, c.hy.) is narrow, and only dilates a little in returning to the 

 basal plate; over the bend, an "extra-hyal" band is separated (ex.hy.). The notch of 

 the basal plate is large, the fonn wide, the lobes only moderately free : a thick crest 

 occupies the middle of its lower face, this expands in front, and is calcified ; behind, 

 >n)CCCLXxxt. 2 I 



