ON THE VERTEBRATE SKELETON. 219 



anterior and anterolateral walls of the cranium, defends the rhinenccphala 

 and transmits the olfactory nerves, but is altogether distinct from and pos- 

 terior to the capsules of the organs on which those nerves are ramified. 

 In the crocodile Cuvier restricts the term ethmoid to the cartilaginous 

 laminae, capsules, or supports of the olfactory ramifications after the nerves 

 have left the cranium. In mammals the ethmoid is made to include both the 

 bones that close the cranium anteriorly, support the rhinenccphala, give exit 

 to the olfactory nerves, and those which defend and sustain the enormously 

 developed and complex superior parts of the organ of smell*. Whilst this 

 confusion is permitted to vitiate osteology, it is plain that no intelligible 

 homological or other proposition can be predicated of the ' ethmoid.' 



When Cuvier, with reference to the hypothetical possibility of the homo- 

 logue of the frontal forming part of the bone r — u in the frog, adverts to 

 the second chance of bringing the ' os en ceinture' into the ordinary cate- 

 gory of cranial bones, by viewing it as the * ethmo'ide, ' he adds, that it would 

 then be " un ethmo'ide ossifie, ce que sera une grande singularity " (ib. 

 p. 388). Here it is obvious that the predominating idea of the ethmoid was 

 that presented to his mind by the capsules of the olfactory organ in the 

 crocodile and other reptiles, which he had so called, and which are wholly or 

 in great part cartilaginous. But the parts of Cuvier's ethmoid in birds and 

 mammals, which are in functional and physical relation with the cranial cavity, 

 rhinencephala and olfactory nerves, are ossified : the bone, also, to which he 

 gives the name ' ethmoid' in fishes (fig. 5, is) is ossified ; and, what is more 

 to the purpose, the bones (n) in fishes, ophidians, chelonians and saurians, 

 which repeat the essential characters of the batrachian ' os en ceinture,' are 

 likewise ossified. 



General homology teaches that the bone or bones in relation to the defence 

 of the rhinencephala and the transmission of their nerves belong to one class, 

 and that the parts of the skeleton, whether membranous, gristly or bony, 

 which form the capsule or sustain the olfactory organ itself, belong to another 

 and very different class of parts of the skeleton. But, not to anticipate what 

 belongs more properly to a subsequent section of this report, observation 

 shows the two parts to be physically distinct in all vertebrates except mam- 

 mals, and to be distinct in the foetus of these. Whether we restrict the term 

 ' ethmoid ' to the neurapophysis or to the sense-capsule (which in mammals 

 constitutes the ' concha? superiores' and cells of the ethmoid), the term must 

 be applied arbitrarily in its extended or homological signification, since the 

 neurapophysis dismisses the nerve by a single foramen or groove in all the 

 vertebrates below mammals. The multiplied foramina in the neurapophysial 

 or cranial part of the anthropotomical ' ethmoid,' whence that name, as well 

 as the special designation of the part called ' lamina cribrosa,' are modifica- 

 tions peculiar to the mammalian class, but not constant here, and they form 

 no essential homological character of the bone in question. It appears to 

 me preferable, since we have two essentially distinct parts of the skeleton 

 combined in the mammalian and human ethmoid, to restrict the term to the 



* Objecting to Oken's idea, that the prefrontal in the crocodile was homologous with the 

 part of the ethmoid called 'os planum' in anthropotomy, Cuvier says, " Or l'os planum ne 

 paroit jamais sur la joue ; il ne se montre plus dans l'orbite a compter des makis si ce n'est 

 un petit point dans les galeopitheques et dans quelques chats. Dans tous les autres mam- 

 miferes 1' ethmo'ide est entierement enveloppe et cache par le palatin" (note that significant 

 connection) " et par le frontal et specialement par cette partie du frontal dont il est main- 

 tenant question et qui se detache dans les ovipares. Le veritable ethmo'ide est enveloppe 

 de la meme maniere dans le crocodile, quoique presque toutes ces parties restent cartilagi- 

 neuses." — Ossem. Foss., v. pt. i. p. 73. 



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