DEVELOPMENT OE THE SKULL OF THE COMMON FOWL. 
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semicircular canal ( a.sc .) : the vestibule (v.b.) is laid open; and the back wall of the cochlea 
shows by transmitted light the cavity itself, and the enclosed lower otoconial mass. 
Mesiad of the stapes the internal carotid {i.c.) is seen as it runs forward to gain the open 
pituitary space; and the section shows also how completely continuous the periotic 
cartilage is with the investing mass (i.v.). This section is viewed from behind ; and being 
somewhat oblique, the left side shows the cochlea ( c.l .) laid quite open, and the curled 
plate of calcareous granules ( ot .) is seen lying in the inner end of the sac. 
The delicate distal ceratohyals (Plate LXXXI. fig. 15, c.h .) have coalesced at both 
ends, a primordial chink being left along the mid line ; the basihyal ( [b.h .), basibranchial 
( b.br .), and the branchials (c.br., e.br .) have assumed much of their persistent form. 
All the membrane bones have commenced, and several of them may be described at 
once ; the relations of the remainder will be seen best in the next stage. 
The premaxillaries (Plate LXXXII. figs. 2 & 2a, p.x.) appear in the thick, soft, fibrous 
investment of the prenasal cartilage (jp.n.) outside the perichondrium; they are trian- 
gular at first, and then rapidly develope their nasal (fig. 2a), marginal, and palatine 
processes (fig. 2), 
The maxillaries * (fig. 2, m.x.) are developed at some distance from the endoskeleton, 
in the fore part of that flap which grows downwards from the maxillary rudiment (see 
Huxley, Elem. Comp. Anat. p. 138, fig. 57 G, l ); they are at first a delicate thread 
of fragile bone, pointed at each end, broad in the middle, and sending inwards, at their 
anterior third, a broad, recurved ear-shaped plate, which nearly touches the base of the 
septum nasi, and is the rudiment of the palatine plate or “ maxillo-palatine.” A much 
smaller style lies in the cheek-flap behind the maxillary ; it is pointed at both ends, and 
its anterior end lies outside the end of the maxillary : this is the jugal (/). Behind the 
jugal is the quadrato-jugal (q.j.) ; it is twice as large as the jugal, passes within it for 
some distance, becomes rather thick, and then curves inwards at its end to articulate with 
the quadrate. The nasals, frontals, parietals (not figured in the illustration of this 
stage) are delicate dendritic deposits in the soft fibrous tissues of the superethmoidal and 
cranial regions ; the squamosal forms a bony eave to the prootic region (Plate LXXXI. 
fig. 14, sq.), and is formed, like the frontals and parietals, in the inner layer of the scalp, 
outside the perichondrium of the related cartilage. 
With all these calcifying membranes every one is familiar; not so with those that 
substruct the base of the primordial skull. 
* In the former paper (Plates yii.-xy.) the maxillaries are everywhere described as “ prevomers,” a term 
strongly inveighed against since by Professor Huxley. At page 113 I spoke of these as the distinct counterparts 
of the palatine plate of the mammalian maxillary. I shall henceforth drop the term “prevomer,” and call 
the Lacertian hone (the so-called turbinal) “ septo-maxillary the hone described as the maxillary in my 
former paper (Plate xi. fig. 1, Plate xm. figs. 12 & 13, mx. p. 141) may be called the “ postmaxillary ” (the 
Fowl does not possess it). I am now satisfied that although many birds have the additional Lacertian bone 
truly represented by maxillary outgrowths, yet these have no existence in the Gallinacese ; and in no bird is 
there a distinct septo-maxillary : the counterpart of the exceptional “postmaxillary” of the Bird must be 
sought for far down amongst the Ganoid Fishes. 
