308 
On the Teeth of the Ox, Sheep, and Pig, 
the capsule becomes the periodental membrane or covering to the 
tooth, and the peiiosteal lining of the bony socket in which it is 
placed — these being also but one.* 
In the pieceding pages reference has more than once been made 
to compound teeth, and to the advantages which result from the 
several constituents of a molar tooth being so arranged as for all 
of them to meet on its wearing surface. From this it might be 
supposed that the dentine, enamel, and crusta,were all brought into 
pressure retains the still existing portion of the outer pulp, which with the 
enamel membrane had been reflected into the cups, in its place. The supply of 
blood to it is kept up by the vessels 
which pass inwards from both the 
capsule and the gum, securely lodged 
in the grooves upon the edge of the 
cusps and likewise in the hollows 
between them. Thus, while the 
tooth is cutting, the process of fill- 
ing the enamel cup with crusta goes 
on. 
The somewhat altered circum- 
stances under which this crusta is 
formed may possibly account for the 
difference observed in the arrange- 
ment of its several parts when com- 
pared with the crusta on the fang. 
Attention was called to this fact 
when the microscopic characters of 
the dentine, enamel, and crusta 
were described. 
The other references to fig. IGare: — a, the capsule, reflected back from one-lialf 
of the tooth, which has also been cut away to show e, an enamel cup ; b, the 
entire half of the tootli covered by the other portion of the capsule, which is seen 
to join the gum above, and to extend downwards to the cud of the forming fang; 
and D, the dentinal pulp cavit}'. 
After a tooth is fully cut, and the crusta upon its imbedded portion also per- 
fected, then the capsule becomes a bond of union betw een the tooth and its socket. 
In this position it is to be viewed both as the pcriuJontal covering to the tooth and 
the periosteal lining of the socket. Much more might be added in further expla- 
nation of these phenomena, but it is unnecessary in a work of this kind. 
* This view of the question of the formation of a tooth has at least simplicity 
for its basis ; for, after all, it is little more than a layer of mucous membrane, 
which is reflected inwards, changed partly in the arrangement of its primitive 
elements, and then reflected outwards again. That portion of the mucous mem- 
brane of the mouth which originally flanked the sides of the dental groove remains 
behind as the lining to the socket of the tooth, while the portion which was reflected 
over the primitive dental papilla again comes to the surface as a covering of 
enamel — the two having now between them a third substance, the crusta, and 
which has been formed by the clianges that each in jii:i-t has undergone. These 
views of the development of the dental tissues will be made the more apparent if 
the series of objects in the diagram (fig. 12) are attentively examined. 
f Fig. IG represents a molar tooth of a calf in the act of cutting the gum — dis- 
sected to show the retention of the matrix of the crusta (the pulp) in the enamel cup. 
A, a portion of the capsule of the tooth reflected backwards ; li, the remaining part 
of the capsule covering one half of the tooth ; i;, an enamel cup ; v f, the cusps pene- 
trating the gum ; c c the gum pressing upon and covering the openings of the 
enamel cups. 
Fig. IG.f 
