i6o 



VETERINARY PHYSIOLOGY 



slate, and then cutting the cord at a lower level when the 

 proprio-spinal fibres connecting the different levels of the cord 

 degenerate. They are chiefly situated in the lateral columns of 

 the cord. 



In man the cutaneous reflexes connected with various groups 

 of skeletal muscles are definitely associated with different 

 levels of the cord. 



Reflex actions in connection with various visceral muscles 

 are 'also connected with the spinal cord. Many of these are 

 complex reflexes involving inhibition of certain muscles and in- 

 creased action of others, some visceral, some skeletal. The best 

 marked of these are the reflex acts of micturition (p. 427), 



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FIG. 80. The neuro-muscular mechanism concerned in the knee jerk, and the 

 time of the knee jerk (A.J.) compared with the time of a reflex action 



(A.R.). 



defseeation (p. 376), erection, and ejaculation (p. 434). 

 The lumbar enlargement is the part of the cord involved. 



The synapses in the cord are not only capable of acting 

 reflexly to set up definite contractions in muscles, but they also 

 exercise a constant tonic action upon them, due to the constant 

 inflow of incoming impressions (p. 42). When this tonic 

 action is interfered with by any condition which interferes 

 with the integrity of the reflex arc, the effect of directly 

 stimulating a muscle is diminished. This is very well seen in 

 the contraction of the quadriceps extensor femoris which occurs 

 when the ligamentum patellae is struck sharply, causing a kick 

 at the knee joint the knee jerk (fig. 80). When the reflex 



