FEesB., 1912. MamMALs OF ILLINOIS AND WISCONSIN — Cory. 15 
Some zo6logists still further abbreviate the formula, giving only one 
side of the jaw, as the number of teeth on both sides are supposed to be 
alike, thus: 
1 2, Cs Pay ® 
ie: 3 
M. 4xo= 50. 
4 
A reference to a single tooth is often written as follows: (Pm. 1) 
and would mean the first upper premolar, or (Pm. 2), which would refer 
to the second lower premolar. 
The variation in the number of teeth in different mammals is very 
great. The Anteaters (Myrmecophagide) have no teeth; the Narwhal, 
for example, may be said to have but one, although there is another in 
a rudimentary state imbedded in the upper jaw. Some Rodents have 
12, others 20; Sloths have 18; Rabbits 28; Man 32; the Armadillo 98; 
and the Dolphin more than too. There is also an extraordinary 
difference in size and shape as, for example, the tusks of the Elephant 
and the enormously developed tusk or ‘“‘horn’’ of the male Narwhal. 
The Vertebral Column, Spinal Column or ‘‘Back-bone,’’ consists of a 
number of bones connected by cartilages. It is generally considered 
as divided into five regions known as the cervical (neck); dorsal 
(back), which supports the ribs; Jumbar (small of the back); sacral 
(between the /umbar and caudal), consisting of several vertebre 
fused together and supported by the pelvic girdles; and the caudal 
or bones of the tail (see illustration, p. 10.). The number of verte- 
bre varies greatly in different mammals. For example, while in 
Man the caudal vertebrez consist of but three more or less rudi- 
mentary bones, the tail of the African Scaly Anteater (Manis) has 
46. 
The Pelvis is the bony framework formed by the pelvic girdles or hip 
bones and including the sacral vertebre. 
The Ribs — The number of ribs varies in different mammals. They 
are curved bones which are movably articulated with the dorsal 
vertebre, and the upper ones are attached to the sternum with a 
cartilage which becomes ossified in but few forms. The lower ribs, 
which are not directly attached to the sternum, are called “floating 
ribs.” 
The Sternum or Breast-bone is a bone, or series of bones (sternebre), 
connected on each side by cartilage with the ribs. In most cases 
these connections remain cartilaginous during life, ossification 
occurring in but few cases. The sections of the sternum vary in 
character and number. The upper part is called the presternum, or 
manubrium sterni of human anatomy; the sections below this (except 
