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428 DENTAL ANATOMY.

shrews, and insectivorous bats, as well as some others of the imgnicnlate
series, it is desirable to have a thorough understanding of it. Cope
maintains ^ that the median and anterior marginal cusps are the homo-
logues of the two external tubercles of the teeth of such a form as H'ty-
po/ophus (Fig. 204), and that the two cusps, which are here homolo-
gized as the representatives of the two external tubercles of this genus,
he proposes to call intermediate tuljercles. JNIivart, on the other hand,
holds" that all the marginal cusps are developed from the cingulum, and
that the true external tubercles have come to occupy a more and more
internal position on the crown—a view which I believe to be correct.
The evidence upon which I base my opinion is to be found bv exam-
ining the teeth of such genera as >Sfi/poIup}ius, Esthouy.r, and Scapanus
of the unguiculate series, and TJri/laeinuH, DkJe/pJtys, Fhdscogale, and
DasyiD-us among the marsupials. In the genera StypolopJnis and Ksfho-
nyx, as we have already seen, the way is paved, so to speak, for the
formation of the two Vs by the appearance of a broad ledge external to
the two main outer cusps and the elevation of the cingulum into a small
cusp at the antero-external angle of the crown, as well as the backward
prolongation of the postero-external angle and its connection with the
postero-external tubercle by a strong ridge. This latter ridge I
regard as the strict homologue of the last upward stroke of the W. In
these two genera the only modifications necessary to produce the W
would be greater separation of the two external tubercles and the pres-
ence of a median marginal cusp connected with them by ridges.
In the genus Scapanus, or hairy-tailed moles, of this country the fourth
superior premolar does not exhibit the W-shaped arrangement in the
same perfection that the true molars do, the anterior
V being rudimental or absent. The cusp at the an-
tero-external angle, however, i.s present, and can be
clearly shown to be of a cingular origin. It cannot
therefore, as Cope supposes, represent the true antero-
external tubercle, in this tooth at least. In the sec-
ond unworn true molar of Basyurvs (Fig. 210) all
the marginal cusps are present, but the median one
is not connected with the two main external tuber-
cles by ridges, leaving the W imperfect. In this
View of the GrindiTig tootli nothing is morc ai)iiarent than the cingular
Surlace of an Un- • • r. ;/ ,i • i i
worn aroiar Tooth of Origin ot all the marginal cusps ; and no one can
tloubt, it apjjcars to me, that they are strictly homol-
J°internair&!"efter-
n'ai;-, anterior aspect ogous witli thc.cusps in a like positiou iu the molars
of the crown.
ot those animals in which the W is perfectly formed.
A careful consideration of the teeth of the genera above mentioned in
my judgment effectually disposes of the whole question, and demon-
strates beyond doubt the correctness of the position here maintained,
notwithstanding the conclusions of so high an authority as Prof. Cope
to the contrary.
Galeopithecus, or the so-called flying lemur, constituting another
' "Mutual Relations of tlie Bunotherian Mammalia," Proceed. Acad. Nat. Sciences
Philadelphia, 1883, pp. 81-83.
^ Journal of Anatomy and Phyaiolocjy, ii. 138, figures, 1868.