774 
ME. AY. E. PAEKEE ON THE STEITCTUEE AND 
My description of these parts will differ considerably from that given in my former 
paper, as in my earlier observations I had mistaken the cellular tissue composing the 
“ rostrum ” for simple cartilage, and the two parosteal tracts behind it (the basitem- 
porals) for ectosteal plates ; the layer of cartilage, also, which I supposed (“ Struthious 
Skull,” p. 117) to form a floor to the pituitary space, has no existence in the Bird. 
Professor Huxley (op. cit. p. 170) first showed that the so-called “ basipresphenoid ” 
of osseous Fishes is nothing but a membrane bone ; in them, and in the Amphibia, a 
thick tract of potato-faucial subcutaneous fibrous tissue is converted into a large beam 
of bone, which runs forwards beneath the nasal region anteriorly, and backwards below 
the temporal region behind. This bone is well developed in the Amphibia (Huxley, 
op. cit. p. 214, fig. 86, B, x), and its posterior or temporal wings are outspread, whereas 
in the Fish they are often turned very sharply upwards. In the chick, in the next stage 
to be described, there is exactly such a tract of bone, but it has formed strong bony 
attachments to the true skull-base ; at present this connexion has begun, but it is slight, 
and easily detached : but, besides this, the osseous matter is in three separate territories, 
instead of being one continuous sheet as in the Fish and Frog. 
The anterior, narrow ossicle, the “rostrum,” is styloid ; it is formed by the conversion 
into bone of the rostral stroma figured in Plate LXXXI. figs. 6 & 7, r.st. ; posteriorly 
osseous matter has run from it into the lower edge of the walls of the pituitary space ; 
here the innermost part of a parosteal tract has become the ectosteal layer to the carti- 
lage, and parostoses, ectostoses, and endostoses all run into each other, the first being 
the “ cue ” to the second and third : this I call the grafting of an exoslceletal splint 
bone upon an endosJceletal region. 
The osseous deposit, so far forth as it has immediate relation to the cartilage of the 
pituitary region, forms a pair of basisphenoidal ossicles — the equivalents of the sym- 
metrical basisphenoidals of the Lizard and of Man ; these are figured as detached from 
the “ rostrum ” in Plate LXXXII. figs. 1 & 3, b.s. ; on the upper surface (fig. 3) it is 
shown how the bony matter creeps round and into the trabecular root*. 
The rest of the basis cranii is quite separable from the thick subcutaneous floor, and 
the breadth suddenly expands behind the pituitary region; so also the faucial portion of 
the fibrous mat is of great breadth (fig. 2, b.t.). In shape this layer is like the leaf of 
a Bauhinia , the “ rostrum ” answering to the leaf-stalk : the posterior margin of the 
bilobate mass is exaggerated, as to distinctness, in the figure ; but in reality the web 
thins out rapidly in front of the exit of the vagus nerves (8): this sudden change in the 
thickness of the cranial floor is very remarkable, even in the adult bird. 
Two large tracts of osseous deposit, the basitemporals, having a somewhat reniform 
outline, have already appeared in this thick fibrous web (fig. 2, b.t.) ; they are elegantly 
* In certain osseous Fishes (for example the Perch, Pike, Gurnard &c.) the prepituitary portion of the basi- 
sphenoidal cartilage is invested by a delicate ectosteal sheath ; this azygous basisphenoid is thus confined to the 
front of the pituitary space through the remarkable development of th q jprootic floor, which takes up so much of 
the investing mass anteriorly. 
