DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 37 



or " symplectic." As a rule a short segment is cut off close to the stapes, the morpholo- 

 gical " pharyngo-hyal ;" this has not taken place, at present, in this young Frog. 



The proximal piece is the medio-stapedial (fig. 10, m.st., i.st.), and it is largely ossified; 

 the distal piece is not ; it is the " extra-stapedial " (e.sf.) — a pedunculated sub-circular 

 disk ; as yet, there is no supra-stapedial band growing up from the inner side.* 



The " cerato-hyal " (figs. 7, 9, st.Ii., c.hy.) is not yet as narrow as it will be, but from 

 hanging by its primary joint under the antorhital region, it now is articulated to the 

 tympanic floor under the columella and beliind the Eustachian opening {eu.), to wliich it 

 now forms the normal boundary as part of the hyoid arch, that is to say, it is behind 

 the " 1st visceral cleft;" over that cleft, outside, the " spii'acular cartilage" is closing 

 round the membrana tympani so as to form the "annulus" (fig. 6, a.ty.). 



The cerato-hyal band still retains an auriform hypo-hyal lobe (fig. 9, e.Ji)j.,h.hy.),hut 

 the basi-hyal conjugation {h.hij.) is still a tract of simple cartilage running into the 

 dilated basi-branchial plate (b.br.) ; attached to this we see on each side the remains of 

 the branchial pouches, and another remnant is seen also on eacli side of the paired 

 hypo-branchial plates {h.br.), which now end in long sigmoid rods {t.hy), the still 

 unossified " thyro-hyals." 



This is the most instructive intermediate stage of these parts I have as yet 

 succeeded in dissecting out ; if the figures of these parts be compared with what is 

 seen in the larva on one hand, and in the adult on the other, the value of this stage 

 will be self-evident. 



The investing bones, the true " parosteal " plates, are nearly all present ; those of 

 the lower arches have been already described. 



The frontals (fig. 6, /.})., by mistake) are now, /or a ivhile, distinct from tlie parietals ; 

 the latter lie over the paired fontanelles, and the frontals cover the larger space (fo.). 

 The nasals, premaxillaries, and maxillaries {)h , j^x. , mx.) are now quite normal, the quad- 

 rato-jugal (qj.) is appearing, and the squamosal (sq.) is acquiring a supni-tempoval plate. 

 Below, the parasphenoid (fig. 7, pa.s.) is quite normal, having all the hinder processes, 

 and there is no j:)ro-parasphenoid. The "vomers" (fig. 7, v.) are thin crescentic plates 

 notched in front. The palatine and pterygoid bones {pa.,pg.) are now quite separable 

 from the subjacent cartilage, but that is only a temporary state of things in most cases. 



Eighth Stage. — 5. *S7i:«// uf Rana halecina {X. America) ; 1;^ inch long. 



This young Frog was about twice the size of the last, but the species are quite 

 distinct ; this is the most welcome intermediate form I have found between the typical 

 R. temporaria and the gigantic R. pipiens. 



The cranium is much more advanced, but it is still unfinished ; in this respect it is a 

 good link between the young R. palustris and the adult R. temporavia. in some 



* In Psendis (" Cystignathidfe ") I shall bo able to show tico earlier stages of the columella than this 

 ^Plates II and 12). 



