270 DR. H. W. MARETT TIMS ON 
part of the tooth these two cones are indistinguishable the one 
from the other, having fused to form a solid mass. The second 
cheek-tooth (Pl. 26. fig. 4), which is the deciduous tooth, is well 
calcified, and on the verge of cutting the gum. It consists of a 
large antero-external cone, the apex of which has an elongated 
cutting-edge, still showing indications of two tubercles. On 
comparison with the model of this tooth at the previous stage, 
this cone appears to be formed by a fusion of the anterior and 
central external cusps. The well-marked median internal cone 
of the earlier stage has now entirely disappeared. The postero- 
external and postero-internal cusps are relatively much smaller. 
Owing to the greater size of the tooth, the excavation of the 
posterior part of the tooth in a forward direction appears to be 
more pronounced. On the other hand, the undermining of the 
base of the antero-external cusp from within outwards, previously 
mentioned, is now scarcely perceptible. No marked trace of the 
external cingulum is present either in this or the preceding 
stage. 
Microscopically, the epithelial neck of the tooth-germ is no 
longer visible; and I have not been able to detect any lingual 
downgrowth such as would suggest that this tooth had any 
morphological successor. 
The condition of the third cheek-tooth has become complicated 
by the presence of infoldings of the enamel. Here again, there 
is a large external cone which has to the outer side of its base 
two minute cusps, which I consider as belonging to the external 
cingulum. The well-marked inner cone, described in the pre- 
ceding stage, appears to have fused by its apex with that of the 
external cone, the two being separated at their bases, giving in 
section the appearance of an elongated foramen. It might be 
thought that this foramen was due to the tunnelling forwards 
of the substance of the tooth from its posterior end, such as was 
found in the second cheek-tooth. Such, I believe, cannot be the 
cause, for two reasons: (1) in the previous stage no trace of any 
tunnelling is observable; and (2) the external and internal 
cones are separated by a deep fissure extending down to almost 
the root of the tooth. This foramen seems, therefore, to be due 
to a fusion of the apices of the two cones cutting off the deeper 
part of the fissure from the surface. This occurs towards the 
anterior part of the tooth. About the centre a communication 
takes place between this cavity and the internal surface of the 
