312 ON THE MANATEE. 
1851,* described the teeth of the Tapir as presenting two peculiarities 
—the one, that the dentinal tubes of the crown of the tooth terminated 
beneath the enamel in oval dilatations, a most unusual manner of ter- 
mination; the other, that vascular canals were to be found in the 
dentine of its roots. 
“The regular oval dilatations which terminate the coronal deciles 
tubes of the Tapir’s tooth are as nothing compared to the great cavities 
into which the coronal tubes of the Manatee’s tooth would pass; and 
where there is one vascular canal in the dentine of the root of the 
Tapir’s tooth there are fifty in that of a Manatee. Yet it is remarkable 
that, besides an external similarity of form, the Manatee’s tooth should 
present what might be called an immense exaggeration of the two 
peculiarities which mark the dental tissues of the Tapir.” 
DESCRIPTION OF THE PLATES. 
Puate 11. (XXVIII) 
Front view of the head of Manatus americanus, representing the extreme posi- 
tions of the pads of the upper lip in the movements described in the letter- 
press. 
Fig. 1. Lip-pads approximated. 
Fig. 2. Lip-pads separated. 
In both figures the nostrils are represented closed. 
Puare 12. (XXIX.) 
The liver of Manatus americanus. 
Fig. 1. Ventral aspect. 
Fig. 2. Dorsal aspect. 
PuaTE 13. (XXX.) 
The brain of Manatus americanus. 
Fig. 1. Longitudinal section in the middle line. 
Fig. 2. Lateral aspect. 
Fig. 3. Superior aspect, the upper part of the right hemisphere having been 
removed. 
Fig. 4. Inferior aspect. 
* “ Proceedings of the Zoological Society,” 1851, p. 121. 
