39Q A MANUAL OF VETERINARY PHYSIOLOGY 



of the body and the condition of muscular tension. This involves 

 the existence of a special muscle sense which plays such an 

 important part in locomotion. In the muscles this sense is 

 represented by special bodies generally found near tendons, called 

 neuro-muscular spindles ; these are from J to J inch in length, 

 and T ^g- inch in width ; each spindle is of muscle surrounded by a 

 sheath, and has a sensory nerve entering it at one end. Nervous 

 structures known as the tendon organs of Golgi, also exist in the 

 tendons at their junction with the muscle fibres ; they consist of 

 spindle-like bodies connected with one or more fine medullated 

 nerve fibres. These nerves are in communication with a portion 

 of the brain which is devoted to the ' muscle sense.' The ordi- 

 nary degree of sensibility in muscle is not very great unless the 

 part be cramped or inflamed, though pain is caused when they 

 are cut into. By means of the motor nerves the muscle is sup- 

 plied with impulses which, originating in the brain, passing 

 thence along the spinal cord, and emerging by the ventral roots, 

 reach the skeletal muscle concerned, and so bring about con- 

 traction. Division of the motor nerves, or interference with 

 their function, causes paralysis of the muscle or muscles sup- 

 plied by them. F^ach motor nerve enters the primitive fibre 

 about its centre, and terminates in a special organ known as an 

 end plate. By means or curari this end plate may be paralysed, 

 in which case stimulation of the nerve leads to no muscular 

 response in consequence of the block, though the muscle itself 

 remains irritable, and readily responds to direct stimulation. 



The question of the nerve supply to muscles will receive 

 fuller consideration when the subject of ' muscle sense ' is dealt 

 with in the chapter on the Senses (Section IV.). It will also 

 engage attention in Chapter XIV. on the Nervous System, 

 when the extremely important subject of reflex inhibition is 

 discussed. It will suffice here to point out that the nerves 

 conveying impulses which pass from muscles, which later on 

 will be known as afferents, are numerous, while the nerves con- 

 veying impulses which pass to muscles, known as efferents, are 

 limited to the transmission of those impulses which stimulate 

 contraction. There is no set of efferents to a muscle which 

 prevent or control contraction, though obviously this is as 

 important as the excitatory impulses which initiated it. How 

 this difficulty is overcome is a matter of future consideration. 



Masses of material built up on the lines described above are 

 intended for the transport of the body, for which purpose they 

 are united to the skeleton either by tendons or by the direct 

 insertion of their own fibres. In the muscles of the limbs the 

 tendon attachment is the most usual, wherever, in fact, the parts 

 are exposed to great strain. There are certain muscles in the 



