794 
ME. W. K. PAEKEE ON THE STEUCTUEE AND 
regained, and has become persistent. This small cup on the outside of the prootic (a 
large distance from the front of the exoccipital) is very similar to that for the short crus 
of the “ incus ” in the foetal Lamb. The Psittacinse make some approach to the Fowl 
in the articulation of the os quadratum. It is in the Fowls — in the Common Fowl espe- 
cially, and in the whole Gallo-anserine series to a great degree — that the basitemporals 
have their most massive development. This is correlative of the abortion of the “ tym- 
panies,” which figure largely in many families of typical birds — the chief of the tym- 
panic chain representing the “ interopercular ” of the Osseous Fish and the crown of the 
inverted arch of the tympanic ring of the Mammal. In the Fowl and in the true Galli- 
naceee (“ Alectoromorphse,” Huxley) I find scarcely a trace of ossification in the tendinous 
ring surrounding the “membrana tympani.” In the Peafowl, however, a tympanic 
appears which is ornithically unique, although many birds have a chain of tympanies : 
this is formed in the posterior part of the shallow “ meatus externus ” (see Memoir on 
Balcenicejps, p. 316), and therefore answers to the posterior part of the bony meatus of 
the Mammal ; and lying as it does directly beneath the posterior process of the squamosal 
“ supratemporal,” it may represent the ichthyic “ opercular” splint-bone*. 
Eighth Stage. — Chickens 3 Months old. 
The parts especially worthy of notice in this stage are the occipital, periotic, and 
posterior sphenoidal regions (Plate LXXXV. figs. 4-7 ; fig. 6 magnified 3 diameters, 
and the others twice the natural size). 
The degree of coalescence of parts at this stage is illustrated by figures of the skull- 
basin. All but the parasphenoidal splints, which are so early engrafted upon the skull- 
base, are separable by maceration ; only the symmetrical premaxillaries and dentaries 
have united at the mid line, the former very early, and the latter soon after hatching. 
In the regions figured several of the smaller sutures are closed, and those that are still 
open are mostly narrow, so that the true shape of the bony territory is well shown. An 
upper and a lower notch still attest the original symmetry of the superoccipital (Plate 
LXXXV. figs. 5-7, s.o.). The exoccipital ( e.o .) has completely absorbed the epiotic, 
which is now a mere region (e.p.). 
The basioccipital ( b.o .) is a thick, lozenge-shaped mass of bone, underlain by the basi- 
temporal below (Plate LXXXV. fig. 4, h.t ., h.o.), and articulating above (fig. 5) with the 
basisphenoid, a notch in the mid line marking the end of the chink-like remnant of the 
“ posterior basicranial fontanelle.” 
The more enlarged side view (fig. 6) should be compared with the like figure of the last 
stage (Plate LXXXV. fig. 2) ; and then it will be seen that the remnant of the epiotico- 
occipital suture is gone, and also the whole of that surrounding the outer part of the 
* I do not wish to push this doctrine of exact representatives, or “ true homologues,” too far ; a perfect 
harmony of the whole splint-category in the Vertehrata generally will he obtained when our knowledge of 
this wide subject is perfect, — and not till then. I may, however, mention a curious modification of the “ prin- 
cipal tympanic ” of the Crows and Singing Birds, namely, that it enrings Nitzsch’s “ siphonrum.” 
