ON THE VERTEBRATE SKELETON. 227 



Cuvier describes the posterior and superior expanded and diverging plates 

 of the prefrontals as "la lame cribreuse de l'ethmo'ide :" the coalesced part 

 forming the septum, he ascribes to the vomer*. Dr. Kb'stlinf, also, who 

 rightly recognises the ethmoid to be no proper bone of the skull, but only 

 an ossified organ of sense, yet describes, after the anthropotomists, the coa- 

 lesced prefrontals as the cribriform and azygos processes of the ethmoid 

 (' Siebplatte' and ' Scheidewand des Siebbeins,' pp. 85. 89) in cetacea which 

 have no organ of smell. In a young balaenoptera, in which the frontals, the 

 vomer and the nasals were ossified, I find the prefrontals as two cartilaginous 

 plates, extending from the nasals above to the groove of the vomer below. In 

 the manatee the essential parts of the prefrontals which close the cranial 

 cavity anteriorly, and give exit to the olfactory nerves, are thick and unu- 

 sually expanded. But in no mammal do these parts, with their continuation, 

 the ' lamina perpendicularis,' which, as the coalesced neurapophysial plates 

 of prefrontals, bring the vomer below in connection with the nasals above, 

 ever undergo such modifications as to obliterate their true and essential ho- 

 mological characters. 



In proceeding next to consider the special homologies of the bones of the 

 arch closed by the premaxillaries (22) and constituting the ' upper jaw,' I 

 commence with the palatines (20), because they form, throughout the verte- 

 brate series, the most constant medium of suspension of that arch to the 

 anterior cranial segment formed by the vomer, prefrontals and nasal. This 

 ' secret affinity,' as Goethe would have termed it, before the knowledge e of 

 the general type had revealed its nature, is manifested by the process of the 

 palatine in man, which creeps up, as it were, into the orbit to effect its wonted 

 union with the prefrontal, to that part of the bone, viz. of which Cuvier had 

 recognised the homologue in his 'ethmoide' of the bird J. It is the very 

 constancy, indeed, of these and other connections which has exempted the 

 palatine from the different determinations and denominations attached to 

 other bones, and which renders further discussion of its special homology 

 unnecessary here. 



Passing over, for the same reason, the maxillary (21) and premaxillary (22), 

 and referring to the excellent treatise by Dr. K6stlin§ for the grounds of 

 the determination of the 'pterygoid' (24), I proceed to notice other bones 

 which, diverging from the maxillary arch, serve to give it additional fixation 

 and strength in the air-breathing vertebrates. The first of these is the malar 

 bone (fig. 11, 20), the homology of which has been traced without difference 

 of opinion throughout the mammalian class ; where, however, the inconstancy 

 of its proportions, number of connections, and very existence, is sufficient to 

 indicate its comparative unimportance as an element of the maxillary arch. 

 It is absent in many insectivores (Centetes, Echinops, Sorex) : it has not 

 been detected as a distinct bone in the zygomatic arch in the monotremes, on 

 account perhaps of its early coalescence, as in birds, with the maxillary 

 (fig. 12, 21, 26): in Myrmecophaga gigantea and Manis, it projects back- 

 wards, as a styliform appendage, from the maxillary, but does not attain the 

 squamosal; whilst in the sloths and their extinct congeners the gigantic 

 megatherioids, the malar presents its maximum of development and complex- 

 ity || . In the DefphinidcB, again, the malar is much reduced : its slightly ex- 

 panded maxillary end forms part of the orbit and joins the frontal ; the rest 

 extending backwards, as a very slender style, beneath the orbit to the squa- 



* Ossein. Foss. v. pt. i. pi. xxvii. fig. 3, h. 



f Der Bau des Knochernen Kopfes, p. 11. 



t See the passage above quoted from the ' Lemons d'Anat. Comp.' ii. p. 580. 



§ Op. cit. p. 328. || Description of the Mylodon robustus, 4to, p. 19. 



