DEVELOPMENT OE THE SKULL IN THE SALMON. 
105 
nian*, the epiotic being the larger and more conspicuous bone. Here, in the Salmon, 
the opisthotic has an average development for a Teleostean; but in the Cod-tribe 
(“ Gadidse ”) it is very large, and reaching down to articulate with the basioccipital, 
ossities the thin protuberant cartilage that encloses the sacculus ; yet in them it is quite 
simple and ichthyic. 
Getting in front of the borrowed part of the encasements of the brain, we come in 
front and at the sides of the pituitary body upon parts that, without a doubt, answer 
to the posterior sphenoid of Man. But in the Teleostean, at best, the basal part, the 
“Turkish saddle,” is very unfinished and the “greater wing” is very small in propor- 
tion to the “petrosal” mass; yet the “ alisphenoids” are unusually large in the Salmon 
for a Teleostean, and it has, what many others do not possess, namely a basal bone. 
The extent of the posterior sphenoid is best seen when part of the skull has been sawn 
off (Plate VIII. fig. 3), and its general form and relation in a transverse section (Plate 
VIII. fig. 4); from beneath (Plate VIII. fig. 2) and within (Plate VII. fig. 4, b.s., al.s.) 
it can be studied instructively. Thus it will be seen that the basal bone is Y-shaped, 
that it leans backwards, that it sets its foot against the end of the orbito-nasal septum, 
and with its arms it props up the alisphenoids. At its bifurcation it leans against the 
prootic floor (Plate VII. fig. 4, b.s., pro.) behind, whilst in front of it the optic nerves 
(2) escape. Between the arms of this bone the pituitary body is let down behind its 
single leg to find no “ seat” to the “ saddle,” save what is formed beneath by the para- 
splienoid ( pa.s .) : the “sella” of the Bird is very similar to this (see “Fowl’s Skull,” 
Plate lxxxii.). The “ alisphenoids,” although in reality forming only the second cranial 
sclerotome, seem as if they would close-in the skull both in the Salmon and the Bird 
(compare the sections, Plate VII. fig. 11, and Plate VIII. fig. 4, with “ Fowl’s Skull,” 
Plate lxxxv. fig. 11). Their relations are complex, and their formation will be better 
understood when we come to their development; the various figures, however (Plate 
VII. figs. 2, 3, 4, 11, and Plate VIII. figs. 1-4), will give a tolerably good idea of their 
architectural relationships. These bones are not brought into relation with the 
“investing mass” as in warm-blooded Vertebrata, but are separated from it by the 
great anterior passage for the “ trigeminus” (see, from within, Plate VII. fig. 4, al.s., 
pro.). Looking at the inner view, we see the alisphenoid propping up the thick supra- 
cranial ridge of cartilage, articulating behind with the prootic, and in front with the 
orbito-sphenoid (o.s.), whilst it rests upon the corresponding arm of the basisphenoid. 
The alisphenoids bound the lateral fontanelles in front (Plate VIII. fig. 1, and Plate VII. 
fig. 3, al.s.,p.fo .); they are separated externally bya thick synchondrosis from the sphenotic 
(Plate VII. fig. 11, and Plate VIII. fig. 4), and externally (Plate VII. fig. 3, and Plate 
VIII. fig. 1) they clamp, as well as underprop, the great cartilaginous “ culmen cranii.” 
The alisphenoids are much more distinct from the beginning from the trabeculee than 
* They soon coalesce in the Turtle ( Chelone my das), and the compound hone, from its relations to the laby- 
rinth, has been mistaken for merely an opisthotic (see Huxley, ‘Anatomy of Yertebrated Animals,’ 1871, 
p. 203). 
