DEVELOPMENT OF THE SKULL TN THE BATRACHIA. 209 



species; it becomes the nasal septum afterwards, the space between the cornua 

 becoming filled up, and often a projecting prenasal spike grows forwards from it. 

 Over the foramen magnum, the occipital ring is completed by the investing mass 

 in the last, but not in this. On each side, save where the ear-balls are intruded, the 

 tvabecula3 have developed a steep wall, with the rudiment of a roof (" tegmen cranii ') ; 

 the two rudiments run up to the short ethmoidal wall. 



Thus there is left one large fontanelle (/o.), oblong for the most part, semicircular 

 behmd, and more pointed in front in the last, and unfinished behind in this. The 

 nasal capsules are not cartilaginous yet ; the eye-balls liave been removed ; the ear- 

 capsules (fig. 9, an.) are fused partially with the chondrocranium ; they are losing the 

 simple ovoidal form, and taking a shape in Avhicli the curves and swellings of the 

 canals (fig. 9, a.s.c, h.s.c, j).s.e.) are seen. 



Below (fig. 10, f.o.), there has been dehiscence of the fruit-hke capsule, and the 

 spindle-shaped space is the new fenestra ovahs ; its occluding (indifterent) tissue 

 will be the stapes. 



On each side of the orbits, in front, an oblique squarish lobe of cartilage grows out 

 of the cranial wall ; these two processes are the " wings" of the ethmoid (ale.), and 

 answer to the "antorbital" of Birds and the "pars plana" of Mammals; close to these 

 we see the rudiment of the post-palatine {pt.pa.). Under these a band passes 

 outwards— the pterygo-palatine, and in fi-ont of the ear-capsules a similar, but longer, 

 band passes outwards to join (or become) the large facial bar or suspensorium 

 {sp.) ; this is two-thirds the size of the whole basis ci'anii. 



This outer plate runs forwards, curving round the inner nostril {in), and ends 

 opposite the middle of the cornu trabecule {ctv.) ; each l)and ends in an oblong, 

 emarginate, obliquely inturned condyle — the quadrate condyle ('/.). 



The hinder conjugating bar curves and twists round the front of the ear-sac; its 

 root is the pedicle ; its rounded elbow the " otic process." 



Half the upper edge of the side plate is occupied by a large, sessile, decurrent Iteaf 

 of cartilage, which turns inwards and just touches the ethmoidal wing (pr.p., ale.). 

 I cannot find that it has, as yet, become fused with it ; under it, the conjugational 

 band is the pterygo-palatine. 



Here the basal plate shows signs of sub-division ; the apices of the trabeculoe {tr.), 

 from which the notochord (nc.) is retreating, are obhquely marked off from the newer 

 investing mass behind, which has not yet finished the occipital condyles nor even the 

 occipital ring. Hence the fontanelle (fo.) reaches from the foramen magnum to the 

 ethmoidal region, where the intertrabecular tract is not evidently raised at the 

 mid-line. 



The auditory capsules (aii.) are lor.ger than in the last, and the interorbital region 

 of the skull is narrower in the middle ; the cornua trabeculoe (c.tr.) are not so 

 pointed externally, nor so definitely decurved. 



The part taken by the intertrabecula in the mid skull is not half as great as in the 



MIXVCI.X.XXI. 2 E 



