DEVELOPMENT OF THE SKULL OF THE COMMON FOWL. 
783 
Horizontal sections through the pituitary fontanelle throw light upon the perplexing 
morphology of this region of the skull*. The lowest of these (Plate LXXXIII. fig. 15) 
shows the internal carotids (i.c.) coming up from below; also the bony ring which 
surrounds the lower part of the pituitary body, the bony matter of which has spread 
right and left, ossifying a thick fibrous band (f.). Behind these “ posterior pterygoid 
processes ” is an open space, from which the gelatinous tissue has been removed, showing 
the formation of the anterior tympanic recess ( a.t.r .) ; and behind this space the section 
passes through the lower part of the “ posterior clinoid wall” (p.cl.), where it is growing 
up from the investing mass (i.v.). Between the moieties of this mass is seen the fore 
part of the “ posterior basicranial fontanelle ” (p.b.f.), which is being walled-in with 
bony matter. Higher up (fig. 16), above the “ recess,” the pituitary space is lined with 
a thin bony layer, which has grown up from below, whilst in front the bony substance 
(the same as seen at p.cl. in fig. 1) is just growing into the cloven “posterior clinoid 
wall.” Behind this wall there is a thin layer of bony matter, which has crept up from 
the-“ posterior fontanelle” (fig. 15, p.b.f.). 
Near the top (fig. 17) the thick cleft clinoid wall (p.cl.) is notched on each side, and 
the bony matter has risen up in front on each side of the notch. 
Another transversely vertical section (Plate LXXXIY. fig. 2) shows, in a very instruc- 
tive manner, the structure of the posterior sphenoid a little further back. The “ poste- 
rior clinoid wall ” (p.cl.) is seen to be connected by an isthmus above the fore part of 
the “ posterior fontanelle ” (p.b.f.) ; the bony matter of the “ posterior pterygoid pro- 
cesses ” (p.r.p.) touches the cartilage mesiad, and helps to roof-in the “ anterior tympanic 
recess” (a.t.r.). 
The moieties of the investing mass (i.v.) are here very steep, and they rest in de- 
pressions on the top of the thickest part of the massive basitemporals (b.t.). This 
section has been made behind the junction of the basisphenoidal outgrowths with the 
basitemporals, and well shows the membranous nature of the latter — the “posterior 
parasphenoids,” the counterparts of the cross bars in the Pish and the Frog. 
A section through the forwardly turned cochlear cavities (Plate LXXXIY. fig. 3, c.l.) 
shows the thickness of the periotic portion of the investing mass (pr.c.), and how the 
prootic ectosteal plate (pro.) is affecting this cartilage above, and the posterior ptery- 
goid processes (pr.p.) are curling round it below. Below this latter plate is seen part of 
the “ anterior tympanic recess ” (a.t.r.), filled with gelatinous tissue. The floor is formed 
* I have spent a large amount of anxious labour upon the development of the sphenoidal region in the various 
types of the Vertebrate skull, and should be glad to work it out independently if time allowed. I will here 
suggest that the condition of these parts in the Fowl’s skull be compared with what is seen in the Marsupial, 
Edentate, and Insectivorous Mammals. 
Let it be noted here that the “ anterior tympanic recess ” is formed of fibrous bony wings which, in the Mar- 
supial, grow directly from the alisphenoidal centre, and in the iDsectivora ( Erinaceus ) from the basisphenoids. 
In Man the “ lingulas ” evidently borrow their bony matter from the extraneous basitemporals ; whilst in the 
Mammalia generally, although these splints are present, yet, as a rule, the lingulae are ossified directly from the 
basisphenoid. 
