DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 135 



than themselves. Below, there is a narrow, above, a wider and widening tract of 

 cartilage, dividing the bony masses of the ear and occiput, which are moderately ex- 

 tended, wholly ossified, and furnished with a large, wide tegmen tympani {t.ty.), which 

 overhangs the vestibule (fig. 7) to an unusual extent. These right and left bony regions 

 I'each to the fore edge of the foramina ovalia, below, which they almost encircle. 



The skull is wide behind, and narrows evenly, with scarcely any bulging up to the 

 axils of the ethmoidal region. The covered fontanelle (fig. 6) is very large ; it reaches 

 to within a short distance of the foramen magnum, behind, and leaves very little 

 tegmen cranii in front. The edges formed by the walls of the skull are straight, and 

 those walls have scarcely any " coping." The converging and slightly bulging inter- 

 orbital walls are unossified from the foramina ovalia to the ethmoidal axils ; in the 

 hinder third of these cartilaginous tracts, the optic fenestra (II.) is seen to be of 

 moderate size. The girdle-bone [eth.) scarcely covers its own territory m front, and 

 behind, only ossifies the axillary or pinched part, reaching some way back below; 

 above (fig. 6) it is imperfect, its halves scarcely meeting at the mid-line. 



The nasal region is entirely unossified, there is no prenasal rostrum, and the pro- 

 rhinals (fig. 7, p.rh.) are well developed ; the subnasal lamina (s.n.l.) is very broad, 

 and the roof (fig. 6) is of normal width. The external nostrils {e.n.) are only half iis 

 wide apart as the internal {i.n.). The palato-suspensorial arch is quite nonnal, both 

 in its cartilage and in its bones {pa., 2'>g-) ; but both the pedicle {pd.) and the quadrate 

 {'l-c.) are short ; the latter is scarcely affected by the quadrato-jugal {q.j.). The Eusta- 

 chian openings (fig. 7) are rather small, and directed obhquely outwards and forwards. 

 The annulus (fig. 8, a.ty.) is a very small crescent, one-third the average diameter. 

 The stapes (fig. 10, st.) is large, ear-shaped, and ossified, except at the edges; it has 

 a strong apophysis. 



The columella has no inter-stapedial segment, the medio-stapedial (in.st.) is pistol- 

 shaped, the large, proximal pedate end not ossified, and the terminal part is a thick, 

 short spatulate extra-stapedial (e.st.), with no ascending process. • 



The mandible (fig. 8, m.mk., cL, cu:) and the hyo-branchial apparatus (fig. 9, c.hy., 

 h.h.hr.,t.hj.) are perfectly normal; the stylo-hyal end (fig. 7, st.h.) is confluent, above. 



The labials {ic.l^.u.l'.) and the investing bones are, on the whole, quite normal — that 

 is if compared with those of a half-grown Common Frog. The fronto-parietals (f.])-) 

 are very wide behind, deficient inside, in front, and on the left side (reversed in fig. 6) 

 behind, are unusually developed over the arch of the anterior and posterior canals. 



The parasphenoid (fig. 7 , pa.s.) is large and normal, but the vomers {v.) are mere 

 films of bone, bordering the inside of the inner nostrils ; they are toothless. 



There are no septo-maxillaries ; the maxillaries {mx.) send up a distinct process to 

 articulate with the "manubrium" of the nasal {n.), which has the normal conchoidal 

 shape, and comes near its fellow, above. 



The pre-maxillary {px.) has united, by its nasal process, with the inner upper labial, 

 so tliat this cartilage, like the lower labial, is partly ossified. 



