BHUFELDT.] OSTEOLOGY OF THE TETRAONIDA. - 667 
parial facets for the pterygoids and beyond the rounded surface for the 
palatine articulation. 
It will be remembered that in the first edition of this monograph the 
writer announced the fact that he had failed to discover the orbito-sphe- 
noids (considered as the neurapophyses of the arch) i. e., they were not 
found as bones that were produced from separate points of ossification. 
Since that time, more than a year ago, I have not had the opportunity 
to look more thoroughly into the mattter, but the series of my skulls 
of the common fowl and those of Centrocercus show the spaces these 
bones occupy in the mature birds to be completely filled in, the posterior 
orbital walls being more or less complete, a fact familiar to all of us, but 
in birds of the year and still younger specimens large vacuities exist 
where these bones should be; moreover, I have in my possession a 
skull of the common fowl] in which the basi-sphenoid sends up on either 
sidetwo delicate bony sprouts that subsequently complete the periphery 
of the circular foramen for the oculomotorial nerve and the optic. Pro- 
fessor Owen seems to think that these are the centres of ossification for the 
orbito-sphenoids, for this anatomist tells us that ‘the bones, 10 (orbito- 
sphenoids), of the third neural arch coalesce with each other, and the cen- 
trum below, protect asmaller proportion of the prosencephalon than in the: 
Crocodile, but maintain their neurapophysial relation to it and to the op- 
tic nerves, below the exit of which they begin to ossify.” (Anat. of Verts. 
Vol. II, p. 46.) _Huxley,in his Anatomy of Vertebrated Animals, page22, 
says, ‘In front of, or above, the exits of the optic nerves the orbitosphe- 
noidal ossifications may appear and unite below with the pre-sphenoid.” 
Professor Parker is even more decided, for this writer informs us that 
‘Above the optic foramen, wedged in between the alisphenoid and the 
interorbital septum, a four-sided bone has arisen in membrane on each 
side, and there is a smaller pair in front of and above the larger, helping 
to fill inthe fenestre left unoccupied by the orbital plates of the frontals. 
These are the anterior and posterior orbitosphenoids (0. s. Fig. 66.) The 
anterior half of the interorbital septum is ossified, the mesethmoid en- 
croaching on the anterior margin of the interorbital fenestra.” (Morph. 
of the Skull, young fowls up to nine months old, page 249.) 
This is very clear, and as Professor Parker is a very careful observer 
and devoted himself particularly to the subject in question, no doubt 
his observation is correct, and. some more fortunate observer than my- 
self will some day detect these ossifications forthe orbito-sphenoids in our 
Tetraonide ; for since they occur in the common fowl, it seems only 
natural that we should look for them in the Galline generally. This 
accounts for the fact that in my drawing in Plate V., Fig. 51, the po- 
sition of an orbito-sphenoid was simply shown. by dotted lines, and 
marked os.; in this same figure Fr. is the “frontal,” ps. the prefrontal 
or centrum of the vertebra, and «x the usual site for the postfrontal—this 
exogenous element, the diapophysis of the vertebra is not here found, 
its position being occupied by a depressed roughened surface for the 
squamous articulation of the mastoid. We have never personally ex- 
amined any bird in our avi-fauna where this bone is seen independent. 
Descriptive ornithotomists, in their studies upon the skulls of Rheide and 
Struthionide, give the presence of this process as occurring free. 
The neural spine of the frontal vertebra follows the example of the 
parietal in being completely bifidated in the younger specimens. As a 
whole it is perhaps the largest segment in the bird-skull—certainly as 
far as our Grouse and Partridges are concerned. Either half of its 
spine presents, projecting anteriorly from the middle, a flattened process, 
directed gently forwards, downwards, and outwards; that at its extrem- 
