574 
REVIEWS. 
and loosely examined, that data , so often erroneous as not to 
be relied upon by fresh investigators, demand a renewed 
search after facts likely in the end to prove the groundwork 
in the same interesting and useful department of professional 
literature. “ I may observe/’ says our author, “ that the teeth 
belong to the system of organs termed the digestive,” one that 
exists where we can detect no organs either of respiration, 
circulation, or even sensation. The teeth are the organs for 
bruising and comminuting the food, and occupy different 
situations in vertebrate animals ; though they are always found 
placed anterior to the true digestive organ — -the stomach. 
But in the Invertebrata “ we have many examples of teeth 
being situated within the stomach .” “ In birds we have a pro- 
vision somewhat analogous to these gastric teeth of the 
Crustacea, in the development of a peculiar organ termed the 
gizzard.” “ The food which is swallowed by the bird first 
enters the crop, where it is retained a sjiort time to be softened 
by the secretions of this organ. From this receptacle it goes 
to the gizzard, passing through the proventriculus , a short 
canal which connects the two cavities together, and where 
the true digestive fluid, gastric juice, is produced. Within the 
gizzard the food is ground down, and mixed at the same time 
with the gastric juice, which enters the organ from the pro - 
ventriculus above. After being sufficiently digested and com- 
minuted, it passes onwards into the intestinal canal.” “In 
this (the fish) tribe we find, for the most part/that the teeth 
are located either upon the membrane of the mouth, or at the 
commencement of the gullet. They are produced by the 
membrane, and are not, as in mammals implanted, by roots 
or fangs into distinct sockets in the jaws. When attached to 
the bones beneath the membrane, which they are sometimes 
found to be, they are so by distinct ossification of their ex- 
panded basis. Occasionally, these teeth are few in number, 
but often they are so numerous as to thickly stud the greater 
part of the surface of the mouth. As in the mammalian class, 
the teeth of fishes present many varieties of form, each being 
suited to the kind of food on which these creatures live. In 
most fishes the teeth are shed and renewed several times 
