22 
THE VETERINARY SCIENCE 
protect the bladder, rectum and other urinary and genital 
organs; also the cranial bones, to protect the vital organ 
called the brain. Irregular bones are found in the spinal 
column and in the joints, such as the knee or carpus hock 
or tarsus, where great strength is required. 
4. Head Bones. — In speaking of the different points of 
importance in connection with the head bones of the horse, 
suppose a cross or longitudinal section of the head is made, 
it will be noticed that it is full of cavities or sinuses. The 
uses of these are to lighten the head and also to warm the 
air as it passes into the nostrils on its way down to the 
lungs. It will also be found full of foramen or small holes 
through which the nerves from the brain and various blood 
vessels pass to the organs situated in the head, such as the 
tongue, lips, and the various glands in and around the head. 
Then there are the cavities in which the eyes are situ- 
ated, one on each side of the head, called the orbital fossa. 
In examining this fossa you will find a small opening or 
foramen, through which the optic nerve passes in coming 
from the brain to the eye. This is the nerve of sight. Then 
the most important part of all to consider is the cranial 
cavity in which that very important organ is situated called 
the brain, which controls all the various functions and move- 
ments of the body. 
Another important point is the situation of the drum of 
the ear. It is situated in the hardest bone found in the whole 
skeleton, called the petrosal. The nerve that gives the func- 
tion called hearing comes from the brain down to the petrosal 
bone and enters by a small foramen or hole into the drum 
of the ear to give hearing. This nerve is called the auditory 
nerve. 
5. Cervical or Neck Bones. — These bones, are seven in 
number. The first and second bones proceeding from the 
head receive special names. The first one is called the atlas, 
from which the head is suspended and to which it is attached ; 
it somewhat resembles the body of a bird with wings ex- 
tended. The next bone receives the name of dentata. This 
is the bone which allows the head to turn in any direction, 
hence it is sometimes called the axis or pivot of the -neck. 
Between these two bones, on the upper side, is the only 
place where the spinal cord is not covered with bone — a spot 
about the size of a twenty-five cent piece. Here is where the 
