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'; ^j?/, the 'upper prefrontal' ; j:)e, the 'perpendicular 

 ethmoid' ; aet, the ' ali-ethmoid lamina' ; ao i , 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 

 genera! 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 



' "Doclo and its Kindred," &c., 4to, p. 87. " Zool. Trans, vol. t. p. 149. 



' ' Basitemporals,' e. jr., as proposed in the memoir "On the Osteology of the Gallinaceous Birds," &c,, Trans. 

 Zool. Soc. vol. V. p. 176. 



