DEVELOPMENT OF THE SKULL OF THE COMMON FOWL. 
759 
The trabecular roots are transversely crested (the somewhat diagrammatic figure 2 
shows this but feebly) ; this is the angle of that bend formed by the early skull called 
the “cranial flexure” (Huxley, Elem. p. 137). 
This crest becomes very large, and is persistent, notwithstanding the after-straightening 
of the cranio-facial axis ; it is connected with the high “ posterior clinoid wall.” The 
anterior, smaller moiety of the cranio-facial axis is bent, first at an acute, and afterwards 
at an obtuse angle ; it is becoming obtuse on the fourth day ; all this fore part is formed 
by the “ paired trabeculae : ” these are flat bands of, at present, soft or simple cartilage ; 
they are now about - x ^q- of an inch in width, and are moderately thick in proportion. 
These bands are gently curved outwards at first, to enclose an elegantly ovoidal membra- 
nous space, the pituitary space (Plate LXXXI. fig. 2, tr., p.t.s.)', this space is enclosed 
by the early coalescence of the symmetrical bands in front of it ; and this coalesced part is 
nearly equal in length to the pituitary region. The trabeculae maintain a similar size to 
their extremities, but at their coalesced part they have begun to form an arched outgrowth 
on each side ; these symmetrical expansions are the rudiments of the “ aliethmoidal ” and 
“ aliseptal ” cartilages of the nasal labyrinth. This broadened ethmoidal part of the 
trabeculae is bent backwards in a rounded manner on itself, so that the remaining 
part of the trabeculae lies on a lower plane, parallel with the pituitary floor, and with 
the free ends looking directly backwards (Plate LXXXI. fig. 1, c.tr.) ; the free ends are 
slightly divergent, and are separated by a space about equal to their own width. 
These free retral ends of the trabeculae are the “ trabecular horns ; ” they form the soft 
skeleton of the “ fronto-nasal lamina ” ( f.n .), and are developed into the “ alae nasi ” or 
“ alinasal laminae,” and do not coalesce to form the intermaxillary axis or “ prenasal 
cartilage,” as I once supposed (see former paper, pp. 121 & 122). The “ fronto-nasal 
laminae ” will have united with the “ maxillary rudiment ” (m.r.) to enclose the 
anterior nares (n.) before the “intermaxillary axis” will be evident: this will be 
described in the next stage. Here one may pause to remark that the nasal labyrinth is 
formed continuously with the primordial cranium, just as is the case with the otic cap- 
sule ; any segmentation that may appear afterwards will thus be a secondary morpho- 
logical process ; and thus the eyeballs are sharply distinguished from the other sense- 
capsules, which, from their undefined skeletal growth, and their relations to the visceral 
arches, form a most puzzling problem to the morphologist. It will be seen from this 
description that the “anterior sphenoidal region” is scarcely at all represented at this 
stage ; for the somewhat narrowed waist formed by the trabeculae immediately in front 
of the pituitary body is all that has yet appeared of the “ anterior clinoids,” the 
prepituitary part of the basisphenoid, and the presphenoid. This latter part is, 
indeed, feebly represented in the adult Bird, and only occupies an angular space above 
the junction of the perpendicular ethmoid with the basisphenoid. At present there is 
a curved, clubbed, subocular bar, the “ maxillary rudiment ” ( m.r .), which comes very 
close at its anterior clubbed end to the “ fronto-nasal lamina,” but has not yet united 
with it to enclose the anterior nares ( n .). In fig. 1 the cartilaginous differentiation of 
