770 
MR. W. K. PARKER ON THE STRUCTURE AND 
the shoulder-plate, in the Pheasant (plate 16. fig. 4, 'p.cr.') it is a distinct segment, later 
and feebler in its chondrification than the main bar. All Birds above the Ostriches 
agree in this ; whilst all the typical Struthionidse have a Reptilian continuity in these 
parts : in this they agree also with certain low Mammalia, e . g. the Monotremata. The 
manner in which the simple clavicular membrane-bone grafts itself upon the detached 
precoracoid of the Fowl is precisely similar to the behaviour of the splints of the skull- 
base of the same and other birds. Like the precoracoidal segment, the basipterygoid 
plates (a.g>.) are late in their appearance, as compared with the rest of the basisphenoidal 
region ; their further development will be described hereafter. Ultimately it will be seen 
that there is nothing in the adult bird to distinguish them from those of the Ostrich, 
their smaller size and more forward position not being of any essential importance. 
In the first stage (Plate LXXXI. fig. 2, tr.) the roots of the trabeculae were seen to 
project outwards; in the next (fig. 8, l.g.) a retral lobe could just be distinguished on 
each side of the pituitary space ; now a very perfect differentiation of this part is manifest, 
and a pair of very notable ear-shaped processes (Plate LXXXXI. figs. 1 & 3, l.g.) are 
seen projecting backwards, one on each side of the deep “ sella turcica.” At present these 
parts are entirely cartilaginous, and present a peculiar appearance ; for the cells in their 
interior are crowded together and full of granules (Plate LXXXI. fig. 16, magnified 250 
diam.), so as to present the appearance of a very dark pith : this is similar to what is seen 
in the persistent trabecular rods of the Ophidia. The remarkable ornithic modification 
which these parts undergo will be described by and by; at present I make bold to 
assert that they answer to the unossified “ lingulae sphenoidales ” of the human embryo : 
they receive their osseous deposit from another source, namely from the azygous para- 
sphenoidal piece * ; but to interpret the primordial skeleton by the after-deposits of 
bone is to study the mask , and not th & face. 
Behind the pituitary space the base of the skull, in its thick part, forms a very narrow 
waist ; and the moieties of this pinched part are also contracted at their inner edge. 
This lateral retreat of the fore part of the “ investing mass ” gives rise to Rathke’s 
“ posterior basicranial fontanelle ” (p-b.f .) ; it is occupied along its mid line by the noto- 
chord (Plate LXXXII. figs. 1 & 3, n.c.) : it is not, as I once supposed, the hinder part 
of the original hypophysial or pituitary space, cut off by the formation of the “ posterior 
qlinoid wall,” but it is a subsequent modification, caused by the opening-up and widening 
of the primordial fissure in which the notochord lies ; for the moieties of the investing 
mass are seen to press closely on the notochord in the first stage (Plate LXXXI. fig. 2) ; 
the chink is larger in the second stage (fig. 8) ; and by the end of the second week a 
wide lozenge-shaped space is formed (Plate LXXXIII. fig. 2, p.b.f.). 
Gradually, as the skull outgrows the notochord, this region becomes the shelving 
postpituitary part of the basisphenoid. 
The thin part on each side of the fontanelle is the root of the alisphenoid ( a.s .) 
* Prom a careful comparison of these parts in the lower Mammalia with those of Man, I feel satisfied that 
the bony “ lingulae” in that Class answer to the “ basitemporal” rudiments of the “ parasphenoid.” 
