768 
ME. W. K. PAEKEE ON THE STEUCTTJEE AND 
is entirely composed of the articulo-meckelian rod. This rod (Plate LXXXI. figs. 5 & 
12, m.k, ar.) is a gently curved very solid bar of hyaline cartilage ; it bulges and narrows 
two or three times, but does not greatly diminish in size even at its rounded anterior end. 
The articular portion is scooped in harmony with the swellings on the lower face of 
the quadrate ; and from this part there project two finger-shaped processes ; these are the 
internal ( i.a.jp ) and posterior (p.a.p.) angular processes. Already these processes show 
the type to which the bird belongs ; for they have a peculiar development in the whole 
“ Gallo-Anserine ” series, and in one or two mixed cognate forms (for instance, in the 
Flamingo) ; they attain their most extraordinary development in the “ Tetraonine ” sub- 
group of the Gallinse, and especially in Tetrao urogallus. 
In a somewhat earlier stage (head of embryo 4^ lines long, see Plate LXXXI. fig. 12, 
12 diam.), notwithstanding the rapid elongation of the Meckelian bar (m.k.), these pro- 
cesses are scarcely more developed than in the Struthious Birds (see former paper, Plates 
vii.-xiv.), and the ends of these short processes are very knobbed. In this instance the 
nascent connective fibres surrounding these parts were quite free from osseous deposit, 
and so was the rest of the primordial skull, now representing the Cartilaginous Fishes ; 
but in one a day or so older the splint-bones had commenced outside the perichondrium 
of the Meckelian rod (fig. 13, su.). Here the upper view of the articular part of the man- 
dible shows that it is a bifurcating or partially double ray, which developes a groove- 
and-ridged articular surface on its upper face, at the point of bifurcation. 
The next poststomal cephalic arch (the hyoid) is slow of growth, feeble in develop- 
ment, and rapidly gains an enclosed position, instead of maintaining its proper surface 
parallelism with the mandibles. The arches themselves (the cerato-hyals) are mere 
distal rudiments, such as we often see in the costal arches, a long space of mere fibrous 
tissue intervening between the arch and the pier. Their chondrification is late , as a 
correlate of their feeble growth. A somewhat earlier and stouter piece of cartilage 
appears between and behind them, the basi-hyal (b.h.) ; it is tear-shaped, with the 
pointed end foremost. Behind this, with its pointed end looking backwards, a longer 
and narrower piece appears ; this is the so-called uro-hyal ( b.br .), an azygous bar answer- 
ing to the basi-branchial series of the Fish-class generally, and not to the “ uro-hyal ” of 
the Osseous Fish — which is a fibrous bone, a “ basi-branchiostegal.” The first branchial 
arch of the Fish is here represented by a stout ray segmented into an upper smaller 
(i e.br .), and a lower larger segment ( c.br .) : these are they that suffer such extraordinary 
development in the Humming-birds and Woodpeckers, and which in typical birds always 
surmount the occipital plane, whilst in the typical Struthionidse (o'p. cit. Plates vii.-xiv.) 
they are arrested at the stage here described in the chick. 
Third Stage. — Head of Embryo from 8 to 9 lines long : middle of 2nd Week 
of Incubation. 
Henceforth my work will fill both hands at once ; for now the skeleton of the skin and 
its enfoldings will everywhere present itself side by side with the proper primordial 
