ON THE VERTEBRATE SKELETON. 229 



birds, does not distinguish 27 from 26, the true 'jugal:' and Geoffroy viewing 

 the ' portion ecailleuse' of the temporal in that cranial bone of the bird, which 

 he figures under the letter R, fig. 17, pi. 27 (Annales du Mus6um, x.), calls 

 the true squamosal, the original separation of which from the malar he had 

 noticed in the chick, 'jugal posterieure.' He did not admit that this division 

 of the zygomatic style was constant or common in the osteogeny of the skull 

 of birds : but I have always found such division in the embryo, and it con- 

 tinues longer than usual in those very species, e. g. the duck and ostrich 

 (fig. 23, 26, 27), in which Geoffroy denies its existence (/. c, p. 361). Oken 

 accurately describes the two constituents of the zygoma in the skull of the 

 goose, in his characteristic and original Essay*, where he calls the posterior 

 piece (27) the humerus, and the anterior one (so) the radius of the head. 

 Bojanusf, who also recognised the fact of the essential individuality of the 

 bone (27) in birds, but who saw the homologue of the squamosal rather in the 

 tympanic (23), calls it ' os zygomaticum posterius.' I could cite other testi- 

 monies to the primitive existence of the distinct bone in birds connecting the 

 malar with the tympanic ; but the fact which chiefly concerns us here is, that 

 if the special homology of no. 8 with the mastoid, and that of no. 2s with 

 the tympanic be proved, we then have a bone presenting the most constant 

 connections of the squamosal in no. 27 : if, however, that name be transferred, 

 as has been done by Cuvier, Bojanus % and Geoffroy, to other bones, then a 

 new bone and a new name must be introduced into vertebrate craniology, 

 for which, as I trust I have shown, there is no sufficient ground. 



Both Oken and Bojanus rightly discern in the permanently distinct bone 

 which, in the crocodiles (fig. 22, 27) and chelonians, connects the malar (20) 

 with the tympanic (2s), the homologue of the bone they call ' cranial hume- 

 rus,' or ' zygomaticum posterius' in the bird. Cuvier is more accurate in his 

 determination of this bone (fig. 23, 27) as the 'squamosal' in reptiles; but 

 again at the expense of his consistency in regard to the characters of his 

 squamosal in the bird: for the homology of no. s (Cuvier's 'squamosal') in 

 fig. 22 with no. 8 (Cuvier's ' mastoid') in fig. 23, is as obvious and unmistake- 

 able as is that of no. 27 (Cuvier's ' squamosal') in fig. 22 with no. 27 (his dis- 

 memberment of the jugal) in fig. 23. The squamosal is relatively stronger in 

 crocodiles than in birds, and in many chelonians resumes its flat, scale-like 

 form ; although, as Cuvier well observes, it answers, in function, only to the 

 zygomatic part of the mammalian squamosal : — " c'est un temporal dont la 

 partie craniale a disparu§." In lizards the squamosal again resumes the zy- 

 gomatic or styloid shape, connecting the mastoid and tympanic with the 

 postfrontal, and usually also with the malar; the posterior connections being 

 here, as in mammals, the more constant ones. 



As the squamosal varies in form with the malar, so it likewise disappears 

 with it in ophidians ; unless the anatomist, tracing it descensively, prefers to 

 see it again in the peculiarly developed hypotympanic of the anourans. Ac- 

 cording to this view of the sudden resumption of its mammalian function in 

 regard to the lower jaw in batrachia, the name 'squamosal' may be trans- 

 ferred to the hypotympanic in fishes ; and, if we must view the pedicle 

 (2s a — d, fig. 5) as ' homologically compound,' and not, like the mandibular 

 ramus, ' teleologically compound,' zsd seems to me a less arbitrary selection 

 from the pieces of that long and subdivided pedicle, for the representative 



* Ueber die Bedeutung der Schadelknochen, 4to, 1807, p. 12. 

 t Anatome Testudinis Europseae, fol. Parergon, 1821, p. 178, fig. 196, i. 

 % The tympanic bone 28 is described in the same work as ' squamosum sive quadrature, ' 

 (fig. 196, g.) : the mastoid is rightly named. 

 § Ossemens Fossiles, 4to. t. v. pt. ii. p. 85. 



