ON THE VERTEBRATE SKELETON. po7 
Cuvier describes the posterior and superior expanded and diverging plates 
of the prefrontals as “a lame cribreuse de l’ethmoide:” the coalesced part 
forming the septum, he ascribes to the vomer*. Dr. Kostlint, 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 balenoptera, 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 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}. 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. Kostlin§ for the grounds of 
the determination of the ‘pterygoid’ (21), 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, 26), 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 
__ aecount 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 Delphinide, 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- 
el 
Te 
* Ossem. Foss. v. pt. i. pl. xxvii. fig. 3, A. 
+ Der Bau des Knéchernen Kopfes, p. 11. 
t See the passage above quoted from the ‘ Lecons d’Anat. Comp.’ ii. p. 580. 
§ Op. cit. p. 328. || Description of the Mylodon robustus, 4to, p. 19. 
