ON THE VERTEBRATE SKELETON. 229 
birds, does not distinguish 27 from 26, the true ‘jugal:’ and Geoffroy v iewing 
the ‘portion écailleuse’ of the temporal in that cranial bone of the bird, which 
he figures under the letter R, fig. 17, pl. 27 (Annales du Muséum, x.), calls 
the true squamosal, the original separation of which from the malar he had 
noticed in the chick, ‘jugal postérieure.’ 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 (J. ¢., 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 (26) the radius of the head. 
Bojanus+, 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. s 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 boue 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 (26) 
with the tympanic (28), 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. s (Cuvier’s ‘ mastoid’) in fig. 23, is as obvious and unmistake- 
able as is that of no. ev (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 anatoinist, 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 
(23 a—d, fig. 5) as ‘homologically compound,’ and not, like the mandibular 
_ ramus, ‘ teleologically compound,’ 2sd 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. 
+ Anatome Testudinis Europe, fol. Parergon, 1821, p. 178, fig. 196, 7. 
' = The tympanic bone 23 is described in the same work as ‘squamosum sive quadratum,” 
(fig. 196, g.): the mastoid is rightly named. 
§ Ossemens Fossiles, 4to. t.v. pt. ii. p. 85. 
