82 
ANATOMY AND PHYSIOLOGY 
fifteenth, while their superior spines, from being thin and 
narrow, and forming an angle of forty-five degrees, 
slanting posteriorly, as in most other animals, become 
more perpendicular, shorter and thicker. Their anterior 
double spines (rudiments of the articulating surfaces for 
the ribs) become more elevated, or nearer to the top of 
the superior spines. When at the fifteenth, these double 
spines disappear, and one short spine is left. The 
fifteenth terminal vertebra is in height, 1 foot 1 1 inches ; 
in width, 1 foot 6 inches ; in thickness, between the 
intervertebral substance, ll| inches ; while the height of 
its body, without the superior spine, is 1 foot 5 inches. 
This fifteenth terminal vertebra has only very slight 
rudiments of the lateral spines remaining, while the first 
terminal has them in length 8| inches, and in breadth 
5 \ inches. From the fifteenth to the twentieth ter- 
minal vertebra there is a gradual decrease in size, losing 
also their upper spines, and becoming nearly round in 
figure. From the twentieth to the thirty-second they 
taper off rapidly, and become somewhat quadrilateral in 
form, with flat indented sides* The last bone of the 
vertebrae is nearly round, and is about 1| inches in 
diameter. 
OF THE SPINAL CANAL. 
In passing through the atlas and dentata, the spinal 
chord is accommodated with a canal of a triangular 
figure, having the base downwards ; it is 8 inches in 
depth, and 10 inches in width at the base. At the 
