354 PROFESSOR OWEN ON THE GENUS DINORNIS. 
exposed the alleged ‘ vertebral body’ gives off a process ‘‘ arching over the foramen, for 
the transmission of the olfactory and ophthalmic nerves.” But this is, surely, a rela- 
tion rather of a ‘ neurapophysis’ than of a ‘ centrum’ of a vertebral segment. 
Some who appeal to developmental phenomena will reject the “‘ general homology ” 
proposed for the interorbital septum by Dr. Melville, on the ground of the non-extension 
of the ‘ chorda dorsalis’ so far forward in the cephalic blastema of the embryo. I may 
presume, however, that the arguments for the insufficiency of this ground of objection 
given in my ‘ Archetype of the Vertebrate Skeleton’ (8vo, p. 6) are held to be conclusive 
by the learned Professor in Queen’s College, Galway. My objections to his view rest 
on the more decisive and demonstrative homological bases of ‘ connexion’ and ‘ relative 
position.’ 
Mr. Parker confines himself to the question of special homology in regard to the 
‘interorbital septum’ of birds, and points out in it, in the illustrations of his paper on 
the ‘‘ Osteology of Gallinaceous Birds,”*—ps, the ‘ presphenoid’ ; eth, the ‘ middle eth- 
moid’ and ‘vertical ethmoid’; prf, the ‘upper prefrontal’; pe, the ‘ perpendicular 
ethmoid’ ; ae¢, the ‘ ali-ethmoid lamina’; ao1, the ‘ upper antorbital’; ao2, the ‘lower 
antorbital.’ 
I believe that all these are but parts of the coalesced ‘ prefrontals,’ including a small 
portion of the rhinal sense-capsule connected therewith; and in regard to the more 
general relations of homology, I retain my conviction that the ‘ prefrontals,’ under all 
their modifications as the ‘ interorbital septum’ in birds, are essentially ‘ neurapophyses,’ 
serially homologous with the ‘ orbitosphenoids,’ and belonging, not to the ‘ third’ cranial 
vertebra, but to the ‘fourth’ or most anterior one. The huge eyeballs in most birds 
press hardly upon the blastemal basis of these poor neurapophyses, interrupting their 
normal development, and squeezing, so to speak, the rhinal sense-capsules out of all 
proper position: hence the value of small-eyed birds with mammalian noses, like the 
Apteryx and Dinornis, in testing the divers notions which the ‘ interorbital septum’ has 
raised in the anatomical mind, and in demonstrating the true and essential nature 
of the part. 
But the interorbital septum is not the only stage on which a supposed plurality of 
bones, with their several denominations, play their parts. Ossification of the blastemal 
basis of the basisphenoid being stimulated to begin by the channels through which the 
blood actively and abundantly passes to the rapidly growing brain, a pair of centres, 
besides the median one, characterize the ossification of this vertebral element in Birds 
as in many Reptiles. Are these parial ossifications superadded vertebral elements, or 
indications of two bones calling for special denominations ?* Considering the varying 
number of points at which ossification commences in the body of a vertebra in the 
* «Todo and its Kindred,” &e., 4to, p. 87. * Zool. Trans. vol. v. p. 149. 
* «Basitemporals,’ e. g., as proposed in the memoir “ On the Osteology of the Gallinaceous Birds,” &c., Trans. 
Zool. Soc. vol. vy. p. 176. 
