PROFESSOR OWEN ON THE GENUS DINORNIS. 351 



with the term ' prefrontal,' nor is it a synonym of ' anterior frontal.' By ' prefrontals ' 

 are meant not only the ' anterior frontals' of Cuyier in Fishes and Reptiles, but also his 

 ' OS en ceinture ' in Batrachians and parts of his ' ethmoide ' in Birds and Mammals : 

 the term ' prefrontal ' is the sign of the settlement of a homological question which was 

 far from being an easy one or of obvious attainment when it became my duty to 

 grapple with it in describing the " Osteological Series " of the Museum under my 

 charge in 1843. Notwithstanding the devotion of twelve pages^ to that subject, by 

 which I believe that now the matter ought to be sufficiently plain. Dr. Melville is 

 unable to understand it. Accepting the choice offered by Cuvier in the skull of 

 birds, he takes the opposite of that to which Cuvier inclined". Seeing that of the 

 three names which Cuvier had given to what I believe to be one and the same bone, 

 two of them were applied to it in pretty equal proportions of the vertebrate series, I 

 balanced for a while whether to adopt ' ethmoid ' or ' anterior frontal.' I considered, 

 however, that by 'ethmoide' Cuvier meant not only the neurapophysial part of the 

 prefrontal, but also the superior portions of the rhinal or turbinal capsules, and that 

 the term, moreover, borrowed from anthropotomy, indicated a structure which, with 

 the two exceptions discovered by me in the class of Birds, was limited to Mammals, 

 and not constant in that class. Inclining, then, to the name referring to the bone in 

 question in Fishes and Reptiles, 1 constructed a term near enough to it to suggest so 

 much of the homology as was true, but sufficiently distinct from it to show that it was 

 not a synonym, but signified something different and much besides. 



In ordinary birds the olfactory nerves, or rather rhinencephalic crura, emerge from 

 the cranium at the upper angle between the hind wall, roof, and septum of the orbit, 

 groove the upper part of the septum as they pass forward to penetrate the prefrontal, • 

 and expand into the rhinencephalon, dispersing the olfactory nerves to the turbinal 

 membranes. The frontal olfactory foramen in Raptores is smaller than the prefrontal 

 one. Between the Vulture and the Crocodile the difference is that the rhinencephahc 

 crura extend along a common canal above the interorbital space in the Reptile, while 

 in the Bird the ossification of the septum divides the rhinencephalic fossa into two. 

 The bones which hold the neurapophysial relation to the rhinencephalon, anterior to 

 the frontals, are the same or homologous in both Ovipara; but in the Bird the 

 secondary peripheral or apophysial developments of the prefrontals are suppressed, as 

 in Batrachians and some fishes {Xiphias), in which they form the anterior wall of the 



' "Ou the Archetype and Homologies of the Vertebrate Skeleton," pp. 46-59. 



'^ "The bone which has heretofore been denominated the lachrymal in birds is undoubtedly the homologue of 

 the prefrontal in the cranium of fishes and reptiles. The true lachrymal bone, which is external to the lachrymal 

 duct, exists in certain Saurians and in the Crocodilidce ; it does not occur in the higher Vertebrates {Aves and 

 Mammalia), while the prefrontal only disappears in certain exceptional instances among mammals ; in birds 

 and mammals it has erroneously been regarded as the true lachrymal, and is so named by the learned Hunterian 

 Professor: this false homology masks one of the most beautiful instances of the unity of organization," &c. 

 (•Osteology of the Dodo,' 4to, p. 87. 1848.) 



