4r ON THE STRUCTURE AND 



mucilaginous or slippery fluid called synovia, which issues 

 from certain glands situated near each joint, for the purpose 

 of diminishing the friction. 



The bones which compose the skeleton present three prin- 

 cipal divisions; the head, the trunk, and the limbs or ex- 

 tremities. In the quadrupeds the head is never wanting. It 

 is placed, (as before observed,) at the anterior extremity 

 of the vertebral column ; and has a free motion in various 

 directions. It is composed of, first, the cranium, which 

 contains the brain, and in the partitions of which are situ- 

 ated the cavities of the internal ear, and frequently part of 

 those of the nose ; secondly, the face, which contains the 

 orbits of the eyes, and the nasal cavities, and terminates 

 below in the upper jaw ^ and, thirdly, the lower jazo. This 

 last is always movable, and from its motions, in aiding the 

 mastication of food, is to be considered one of the most im- 

 portant members of the animal body. The elongation of the 

 head of quadrupeds increases in proportion as they recede 

 from man ; and this elongation in most of them is such that, 

 were they to stand upright, the head could not be preserved 

 in equilibrium, unless the mouth were turned upwards, and 

 the eyes turned back. When standing on its four feet, the 

 head of a quadruped is not, like that of man, capable of 

 being retained upon the spine by its own weight, but is 

 principally kept in its place by a peculiar ligament at the 

 back, (wanting in man,) called the cervical ligament. In 

 the base of the skull there is a large hole, through which the 

 brain unites with the spinal marrow. 



The trunk is formed by the dorsal spine, the ribs, and the 

 breast-plate or sternum. The dorsal spine is a sort of co- 

 lumn, formed by a number of bones, called vertebrce, which 

 are joined to each other by ligaments that admit of a slight 

 degree of motion. Those ribs which proceed from the ver- 

 tebrae and join the sternum are denominated true ribs ; and 



those 



