146 
ON THE ORGANS OF DIGESTION, &C. 
its secretions into the corresponding pouch, and must be 
considered as the parotid. They are formed chiefly by 
the buccinator muscle, and are supplied by branches of the 
facial nerve. 
The teeth of the Ornithorynchus have generally been 
described as four in number, that is, four large grinding- 
teeth, placed two in either jaw, at the entrance of the 
cheek-pouches: but some anatomists seem to have over- 
looked four narrow, horny !>odies, placed over the maxil- 
lary boneSj in the same ihie with the grinding-teeth, but 
anteriorly to them. They are about ^^ths of an inch in 
length, and ''^^oth where broadest. They are composed of 
a horny substance, and are evidently of the same nature 
with the true grinding teeth : they are to be considered as 
corresponding to the smaller grinders of the Mammalia *. 
The structure of the larger grinding teeth has been con- 
sidered by M. CuviER as the most extraordinary amongst 
quadrupeds. They are said to be composed of a great 
number of small, straight, and parallel tubes, so that the 
surface of a transverse section resembles absolutely that of 
a bamboo-cane (jonc a canne ) : these tubes are not closed, 
and the tissue of the tooth is compact only at the triturat- 
ing surface : there is no large cavity in the interior of the 
tooth. These peculiarities in structure, described from the 
teeth of the Orycteropus, may readily be distinguished in 
the larger grinding teeth of the Ornithorynchus. These 
on their grinding surface were very much hollowed out, 
instead of being tubercular ; they may be fairly considered 
as connected with the integuments only, since their struc- 
ture is so different from the teeth of all other animals, and 
• I have made no mention here of the two teeth which are implanted 
into the tongue, an J \vhich were described with that organ in a former 
memoir 
