DEVELOPMENT OF THE SKULL IX THE BATRACHL\. 7'.) 



Thus in a side view (Hg. 4) tlie wall is about half of it bony, but this is due to the 

 curling over of the roof; the " sphenethmoidal " wall itself is quite unossified. The 

 orbito-sphenoidal region is largely fenestrate {o.s.f.), as in Lizards, but in a very different 

 manner. 



In this stage the fontanelle (fig. 2,yb.) is seen in front between the diverging ends 

 of the frontals, and behind, as a lozenge-shaped space {fo'.) between the frontals and 

 parietals. 



Laterally, the ear-capsules are veiy large relatively (compare Plate 11, figs. 1-3; 

 and Plate 12, figs. 2-4) ; and tlie tegnien tympani with the enclosed horizontal canal 

 {t.ty.) projects much in front ; this part is not ossified. 



Below (fig. 3), the two unossified vestibules, embraced at theii- inner margin by the 

 large grooved ex-occipitals, resemble a pair of symmetrically imbedded acorns, the 

 rough " cup " being bony, and the smootli " fruit " cartilaginous. 



Each of these capsules is fenestrate, and operculate, obliquely ; the opercular stapes 

 {st.) looking outwards and somewhat backwards; the rough "cup" is perforated in 

 two places for the glosso-pharyngeal and vagus nerves (IX., X.). In front, the bony 

 matter scai-cely reaches the 5th nerve (V.) ; the optic nerve (II.) passes out of the hind 

 part of the orbito-sphenoidal fenestra, and the olfactory escapes through the closing 

 wall in front. 



The fore part of the tegmen cranii is rather long ; laterally, it is articulated to 

 the ethmo-palatine {e.pa.) ; in front, it passes into the two narrow crescentic na.sal 

 roofs (fig. 4, al.sp.), which are partly covered by the small ear-shaped nasal bones («.). 



The nasal floor (fig. 3, s.n.l.) is of the normal breadth, and in front it is now a finished 

 structure, elegantly crenate, with seven lobes. 



The outer of these ai-e the outer angles of the trabecular cornua, now finishing the 

 nasal floor in front. Next to these, but on a higher plane, are the horns of the nasal 

 crescents {s.n., al.sp.). Near the mid-line we see a pair of short inturned pointed 

 " pro-rhinals " [p.rh.) ; and now, at the middle, there is a little bud of cartilage, the 

 prenasal {p.n.). 



Besides the nasal roof-bones («.), there are now, below, two oval dentigerous plates, 

 placed transversely and some distance apart ; they touch the inner nostril {i.n.) by theii* 

 outer edge ; these are the vomers {v.). 



The semi-oval outline of the face is now nearly finished by the dentigerous pre- 

 maxillaries and maxillaries (fig. 4, px., mx.) ; most of the maxillary bone is moulded 

 on a cartilaginous bar, which is quite unlike anything seen in the last stage. 



The solid ethmo-palatine bar (Plate 11, fig. 1 ; and Plate 12, fig. 1, pt.pa.) is now 

 (Plate 12, fig. 4, e.jxi., pt.pa.) a slender rod, flatter below than above, and in.stead of 

 being curved forwards outside, it is turned suddenly backwards. 



The prepalatine spike (fig. 3, lyr.pa.), which turned directly inwards in the second 

 stage and touched the trabecula (Plate 1 1, figs. 1-3) now has its outer margin coincident 



