DEVELOPMENT OF THE SKULL OF THE COMMON FOWL. 
765 
cavity being continuous, between the narrow palatines, with the plicated nasal sac, 
although the chink between the rostral stroma ( r.st .) and the anteorbital plate is very 
narrow. 
Seen from the outside, the alisphenoid ( a.s .) shows an oblique crest ; this is the post- 
frontal plate (])■/•) ; it is largely developed in Fishes, but entirely absent (as is also 
the alisphenoid itself) in the Lizards and Chelonians. Infero-laterally the cartilage 
of the auditory region is scooped to form the tympanic cavity ; but at present this part 
is filled with a gelatinous stroma, which grows very rapidly for a week or two and is 
then absorbed. The horizontal ( h.s.c .) and posterior (p.s.c.) semicircular canals now 
shine out through the occipital cartilage, and the exoccipital region ( e.o .) has developed 
its tympanic wing. 
The quadrate cartilage (y.) has received a large and peculiar development, and, like 
the uncloven orbito-nasal septum, has attained a struthious condition. Anteriorly the 
little nodule figured in the First Stage (Plate LXXXI. figs. 1 & 2, g.) has grown into an 
arched blunt-pointed “ orbital process ; ” inferiorly it has become a thick bar with two 
oblique condyles for articulation with the mandible ; whilst posteriorly it has grown into a 
long arched crus, which not only articulates with the periotic capsule, above the junction 
of the prootic and opisthotic regions, but also with the exoccipital in front of the root of 
its tympanic wing. This articulation is shown in fig. 5 a (16 diam.) and fig. 5 (6 diam.), 
and it is seen to answer to what is depicted in my former paper on the Ostrich-tribe 
(Plates vii.-xiv.); in the Tinamou (Plate xv. fig. 1, g.) some recovery of the original 
position is attained *. 
Where the quadrate cartilage articulates with the cranium, the side wall is somewhat 
scooped ; but further down two small clefts appear, which, however, never go beyond 
the condition of fenestrse: these are the “fenestra ovalis” and “f. rotunda” (or f. ves- 
tibuli and f. cochlese). The fenestra ovalis is, properly speaking, an aperture in the 
fundus of the cup-shaped articular cavity in which the head of the stapes (Plate LXXXI. 
figs. 5 & 5 a , st.) is articulated, and is morphologically like the acetabular fenestra of the 
Bird, and the glenoid fenestra of the Proteus and Cryptobranchus (see ‘ Shoulder-girdle 
and Sternum,’ pi. 3, figs. 1 & 3, gl.). 
From the first the parts of the hyoid arch are very inferior in size and later in deve- 
lopment than those of the mandible ; at this stage, after the quadrate has undergone so 
much modification and is so well chondrified, the stapes can only now be distinctly seen ; 
and its outgrowths are mere bud-like projections from the main shaft. It is seen that the 
* I must insist on the zoological importance of this condition of the quadrate, which is temporary in the FowJ 
and persistent in the Struthionidse : in a large number of Birds the head of the quadrate, instead of being single 
as in the Struthionidae and in this early stage of the Fowl, is divided into two short crura, one of which (the 
antero-extemal) keeps its normal place on the prootic, whilst the postero-internal crus retains the acquired 
(struthious) relation with the exoccipital ala. The Parrots come nearest to the Fowls in the forward position 
of both the articular facets, which are separated by a very narrow tract ; in both these types the inner is slightly 
behind the outer. 
