The Locomotor Apparatus. 323 



fore and hind limbs with the body, has until recent years 

 been the cause of considerable error being promulgated. 

 It was previously supposed that the muscular attachment 

 of the fore-leg to the trunk indicated that the body was 

 simply slung between the fore-legs, the latter acting as 

 props whilst the hind-limbs did the work. Instantaneous 

 photography has shown us that the fore-limbs not only act 

 as props, but also as most efficient propellers of the body, 

 especially in the gallop, where by measurement it has been 

 shown that one fore-leg will propel the body a distance of 

 10 feet and raise its centre of gravity 4 inches.* 



By means of the fore -legs the horse is enabled in draught 

 to assist his hind-legs in stopping weights. 



Joints are formed wherever two bones come into contact. 

 Dealing only with those joints found in the limbs, which 

 are of the most practical interest, we find we have ball-and- 

 socket joints (as in the hip), hinge-like joints (as in the 

 hock), gliding joints (as in the knee), and spiral joints (as 

 in the stifle). All these joints are coated with articular 

 cartilage and lubricated with synovia. 



Synovia is a viscid, yellow, alkaline fluid containing pro- 

 teids, mucin, and salts. The viscidity of synovia is due 

 entirely to the mucin it contains, and it confers on synovia 

 its slippery nature. There is no difference between the 

 synovia of joints and that of bursse. 



It is said that the amount of synovia in a joint is greater 

 in animals at rest than in those at work, but its bulk 

 appears to be due to an increase in the watery material, 

 whilst the proteids are decreased ; the salts, on the other 

 hand, especially those of sodium, exist in a larger propor- 

 tion than in the synovia of working animals. 



The bursas in the limbs of the horse are very important 

 structures. They are placed where the tendons pass through 

 bony channels, as at the back of the knee, and also may be 

 turned to useful advantage as pulleys, as in the sesamoids 

 at the fetlock, or the calcis in the hock. Without them 

 the rapid movements of the limbs would be impossible, 



* < The Horse in Motion ' (Stillman). 



21—2 



