1896. ] ON MAMMALIAN DENTITION. 557 
Nitzsch in Trachyphonus and Picus and it also exists in Iyna and 
Rhamphastos. 
A further likeness between the three families of birds concerned 
is in the surrounding of the oil-gland by the spinal tract. This 
occurs, as will be seen from Nitzsch’s figures, in both Picus and 
Rhamphastos. 
If Nitzsch’s figures of Capito (Micropogon) cayennensis are 
correct, we may have in the pterylosis a means of differentiating 
the Old World from the New World Barbets. For in the latter 
the posterior part of the spinal tract is separated from the anterior 
and is composed of two distinct limbs which only join just at the 
oil-gland. I would further point out that the identity in the 
pterylosis of Megalema and Cyanops is against their generic separ- 
ation. On the other hand, the pterylosis of Xantholema rosea is 
very different from that of Megalema, which justifies its retention 
as a genus. 
There is the usual interscapular fork, but there is no break, a 
rhomboidal apterion being enclosed, as is so far correctly shown in 
Nitzsch’s figure; but although the two halves of the spinal tract 
do join, the junction is produced only by their lying close side by 
side and they immediately diverge to end at the sides of the oil- 
gland. The tract, in fact, has an hourglass-like shape, which is 
merely an exaggeration of that which, according to Nitzsch’s figure, 
characterizes the Toucans. 
In the lateral and femoral tracts Xantholema agrees with Mega- 
lema. I find, after examining Selenidera maculirostris and Aulaco- 
rhamphus prasinus, that all the Toucans do not agree with Nitzsch’s 
figures of Rhamphastos erythrorhynchus. In the two just-men- 
tioned birds there is no break in the spinal tracts, which are thus 
more like those of Xantholema. The femoral tracts do not arise 
from the spinal tracts so high up as is figured by Nitzsch, and the 
lateral tract, apparently absent altogether from Aulacorhamphus, is 
very rudimentary in Selenidera, consisting of only three or four 
feathers. 
3. Contributions to the Study of Mammalian Dentition.— 
Part II. On the Teeth of certain Insectivora. By M. 
F. Woopwarp, Demonstrator of Zoology, Royal College 
of Science, London. 
[Received May 5, 1896.] 
(Plates XXIII.—XXVI.) 
In their general organization the Insectivora are undoubtedly 
very primitive, consequently one might reasonably expect to find 
their dentition in a similar lowly state. This at first sight appears 
to be the case, at least so far as the pattern of the molar teeth is 
concerned, for if we accept the tritubercular form as the primitive 
1 For Part L., see P. Z.S. 1893, p. 450. 
