PROCEEDINGS OP THE PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
189 
related to each other by the formation of the lower jaw, its 
•articulation not with the skull directly but through the 
intervention of a special bone, the articulation of the 
skull with the spine, position of the ankle-joint, and other 
points of structure. 
Unfortunately, comparative anatomy has received a bad 
name. It is looked upon as an uninteresting subject, 
fit only for an enthusiast. There is some apparent 
foundation for this popular belief, but only when we 
begin the study in the wrong way. To read through a 
work on comparative anatomy is a severe task, but the 
difficulty disappears when we use the book simply as a 
signboard to direct our practical investigations. So im¬ 
portant is this practical part for the derivation of the full 
benefit and pleasure from the study, that Professor Huxley, 
in his Introduction to the Study of Zoology, says that 
“‘unless the student intends to examine the various parts of 
the animal for himself, he had better shut the book.’’ A 
little repugnance is felt at first iu handling dead animals, 
but with a little determination this is easily overcome. 
I have chosen for this evening’s paper a small but not un¬ 
important part of anatomy, and, with the aid of specimens, 
I hope to be able to show that it is not so uninteresting as 
some imagine. Before giving a description of the different 
teeth, it is necessary to have some idea as to what a tooth is, 
and of the structure of an ordinary tooth, as this will simplify 
what is to follow. To give a definition is always a difficult 
matter, and not less so where it appears easiest. We all 
know what a tooth is, but cannot tell another. It is a 
hard substance placed in or near the mouth, and is found 
only in the Yertebrata (the “ teeth” of the Invertebrata are 
not the homologues of vertebrate teeth, but are frequently 
modified limbs). Teeth present a great variety of form 
and structure, and are used for seizing, tearing, pound¬ 
ing or dividing the food, as weapons of offence, means of 
anchorage, or aids to locomotion. 
Structure of a Tooth. —A tooth is divided into three parts 
—1st, the crown or exposed part; 2nd, the fang, or part 
implanted in the jaw; and 3rd, the neck, or constricted 
part between the crown and the fangs. It is composed of 
three substances—1st, dentine, forming the body of the 
tooth, and surrounding the pulp chamber; 2nd, enamel, 
forming a cap for the exposed part; and 3rd, cement, 
covering the fang. These differ from each other in struc¬ 
ture, dentine being formed of minute tubes running 
more or less regularly from the pulp outwards, enamel 
of irregular hexagonal prisms, and cement of a sub¬ 
stance closely resembling bone and containing bone- 
cells. These tissues have a different arrangement in some 
animals, and all are not always present. Teeth, being the 
hardest parts of the body, are frequently the only 
remains of extinct vertebrates, and being intimately 
related to the food and habits of the animal, are of great 
value to the geologist in forming his classifications. 
Fish.— The teeth of fish offer a greater variety in form, 
number, and position than those of any other class. In 
some they are as fine as hairs and almost as flexible; in 
others large, massive, and strong. Many fish, such as 
the common sturgeon, have no teeth; while others have 
thousands. In the latter case, they may be found on 
every bone entering into the formation of the mouth. 
There is a continual development during the life of the 
animal, new teeth replacing those shed or lost. The 
following are examples of some fish dentitions. In the 
lamprey ( Marsipobranchii) there are no true calcified teeth, 
but simply horny cones. In the pike, teeth are carried on 
the intermaxillary, vomer, palate, and lingual bones, 
branchial arches, and lower jaw. Its mouth may be said 
to bristle with teeth. Amongst those on the lower jaw 
are some much larger and stronger than the rest. A 
pike seizes the bait with these large teeth, and retains it 
for some time before attempting to swallow it, and so firm 
is its hold that the angler frequently imagines the fish to 
be firmly hooked, but is soon disappointed to find it let go 
the bait. Any one who has been unfortunate enough to 
get his fingers entangled in the mouth of a livingpike has had 
a very touching illustration of how small a chance of escape 
its prey has got. The structure of these large teeth is 
peculiar. Internally, they are composed of vasodentin e, 
with a layer of unv?tscular, and covered with a trans¬ 
parent substance supposed to be enamel. In the sea- 
angler (Lophius piscatoriusj, a fish with an enormous 
mouth and head and disproportionately small body, the 
teeth are larger than in the pike, and much curved back¬ 
wards. The large teeth of the lower jaw are remarkable 
for the manner of attachment to the jaw. Instead of 
being anchylosed as in ordinary fish, they are attached 
along the posterior border of the base by strong ligaments. 
This allows the teeth to bend backwards but prevents their 
going in the opposite direction; and thus allows great free¬ 
dom of entry to the prey, but effectually prevents its 
getting out again. The fish being very sluggish, it is 
necessary that when once it seizes its prey there should be 
no escape, and of this there is little chance. In the wolf¬ 
fish (Annarrichas lupus J, the teeth in the front of the 
jaws are strong, and project outwards, giving to the animal 
a savage appearance. Those at the back are broad and 
rounded. The use of these teeth is perhaps best explained 
by telling the contents of the stomach of one I examined. 
It was rather a miscellaneous collection. There were parts 
