49 Anatomy Applied to Medicine and Surgery. 



different neurones, but also contains centres, such as a 

 trophic, a reflex and a vasomotor centre, situated in the 

 H-shaped central grey matter. 



Levels of Centres in Spinal Cord. Peterson 

 states that each separate segment of tihe cord ihas> its own 

 particular functions, as, for instance, the reflex centres 

 for the bladder and rectum are situated in the fourth and 

 fifth sacral segments; that for the ankle clonus, in the 

 fifth lumbar segment; the centre for the knee jerk, in the 

 third lumbar, and those for the wrist and elbow jerks in 

 the sixth cervical, etc. Motor and trophic functions are 

 distributed in the same manner, i.e., segmentally, so that, 

 the intrinsic muscles of the foot are represented in the 

 first and second sacral segments ; the knee flexors, in the 

 fourth and fifth lumbar segments ; the thigh muscles, in 

 the second and third lumbar; the abdominal and spinal 

 muscles, from the second to the twelfth dorsal ; the thumb 

 and finger muscles, in the eighth cervical and first dorsal ; 

 the forearm muscles, in the sixth and seventh cervical ; 

 the shoulder muscles, in the fourth and fifth, and the neck 

 muscles in the second and third cervical segments. The 

 sensory distribution is also segmental, thus anaesthesia of 

 the perineum, scrotum, rectum, vagina, and the posterior 

 surface of the penis, is produced by a lesion situated in the 

 fourth and fifth sacral segments. If the lesion be higher 

 up the cord, say at the third sacral segment, the anaes- 

 thesia extends farther out on the buttock and downwards 

 over the back of the thigh. If higher still, as at the fifth 

 lumbar segment, the anaesthesia includes, in addition to 

 the preceding areas, the outer sides of both legs. The 

 lower part of the abdomen corresponds to the first lumbar 

 segment; the umbilical region to the tenth dorsal seg- 

 ment, etc., and when the eighth cervical is affected, the 

 anaesthesia is complete, below a girdle about itihe nipples, 



