DEVELOPMENT OF THE SKULL IN THE BATEACHIA. 
125 
former (st.) is a solid, sub-pedunculate mass, sub-oval in form, but scooped to receive 
the columella. This latter part has no separate inter-stapedial segment; but there 
is a large thick unossified lobe to the end of the medio-stapedial (m.st.) which 
represents it. Between this and the main stem there is a deep notch, faced fore and 
aft with cartilage, then the bony bar gradually lessens, is arched, and ends in a terete 
rod of cartilage which dilates into the thick, oval, bi-convex extra-stapedial ( e.st .). 
From the inner face of this lobe there arises, at a sharp angle, the terete, stout supra- 
stapedial ( s.st .), which is confluent with the “tegmen ” above. 
The stylo-hyal end of the cerato-hyal (figs. 2 and 4, st.h., c.hy.) seems like a flabelli- 
form continuation of the vestibule; it is wide at first, then narrows as it passes directly 
outward, margining the Eustachian opening; is then wider again as it creeps along 
the inside of the quadrate, and after this becomes a little less again, as it passes, 
sigmoid in form, to the hypo-hyal region ( h.hy .). There is no enlargement, but it 
forms a round loop, and then gently dilates as it passes into the basal plate 
(fig. 4, Khrbr.). 
The antero-posterior extent of the basal plate is small, as in the “ Hylidse its lobes 
are large, the foremost fiabelliform, the hindmost-— here quite as large—is stalked 
and emarginate. There is no bone, save in the “ thyro-hyals ” (t.hy.); they are of 
moderate length, divaricate well, are stout, and soft-footed. 
This skull, with its strong roof and sides, is constructed, externally, of seven pairs 
of bones, and an odd one ; in the young the main roof-bones were divided across, which 
gives seventeen “ parostoses ” originally investing the proper endocranium ; the plates 
applied to the cartilage, and grafted upon it, are not counted, but the two “ dentaries ” 
in the lower jaw bring the sum up to nineteen. The other bony tracts in skull and 
face amount to seven pairs and an odd one—that, however, the girdle-bone, was double 
once, so that there are sixteen bony centres that are properly “ endoskeletalin all, 
there were thirty-five ; there are thirty-two bones in this skull. 
But the “ quadrato-jugal ” is grafted on the quadrate and becomes partly endo¬ 
skeletal, whilst, on the other hand, the bony centres that were formed in the chondro- 
cranium (ex-occipital, prootic, &c.), are largely recruited, in their growth, from the 
perichondrial layers of membrane, thus they link on to the palatine and pterygoids 
that begin in membrane, and get their “endosteal” additions afterwards. But the 
truly parosteal “sub-species” of bony centre concerns us now; I shall describe this 
group, and then show what wa,s the form of the original “ chonclrocranium,” on and 
in which this strong architecture is perfected. 
Behind, the roof-bones come close to the edge of the foramen magnum ( fm .), and 
are built across from side to side, without interruption, over the condyles of the 
quadrate region; the hind margin of this wide tract is emarginate, crescentically. 
Ihe nasal, frontal, and saggital sutures form one line of division from snout to 
occiput, and each region of this long suture is about equal. The two pairs of main 
