644 CENTRES IN THE SPINAL CORD. 



In goats and cats, this centre, even after being separated from the medulla oblongata, can be 

 exdtoa directly by dyspnoeic blood, and also reflexly by the stimulation of sensory nerves, e.g., 

 the median, especially when the reflex excitability of the cord is increased by the action of 

 strychnin or atropin (Luchsinger). For the dilator centre in the medulla oblongata, see 

 S 367, 8. 



2. The ano-spinal centre, or centre controlling the act of defaecation. The 

 afferent nerves lie in the hemorrhoidal and inferior mesenteric plexuses, the centre 

 at the 5th (dog) or 6th to 7th (rabbit) lumbar vertebra ; the efferent fibres arise 

 from the pudendal plexus and pass to the sphincter muscles. For the relation of 

 this centre to the cerebrum see 160. After section of the spinal cord [in dogs], 

 Goltz observed that the sphincter contracted rhythmically upon the finger intro- 

 duced into the anus ; the co-ordinated activity of the centre therefore would seem 

 to be possible only when the centre remains in connection with the brain. 



3. The vesico-spinal centre for regulating micturition, or Budge's vesico-spinal 

 centre. The centre for the sphincter muscle lies at the 5th (dog) or the 7th (rabbit) 

 lumbar vertebra, and that for the muscles of the bladder somewhat higher. The 

 centre acts only in a properly co-ordinated way in connection with the brain 

 ( 280). 



4. The erection centre also lies in the lumbar region ( 436). The afferent 

 nerves are the sensory nerves of the penis ; the efferent nerves for the deep artery 

 of the penis are the vaso-dilator nerves, arising from the 1st to 3rd sacral nerves, 

 or Eckhard's nervi erigentes while the motor nerves for the ischio-cavernosus 

 and deep transverse perineal muscles arise from the 3rd to 4th sacral nerves ( 356). 

 The latter may also be excited voluntarily, the former also partly by the brain, by 

 directing the attention to the sexual activity. Eckhard observed erection to take 

 place after stimulation of the higher regions of the spinal cord, as well as of the 

 pons and crura cerebri. 



5. The ejaculation centre. The afferent nerve is the dorsal of the penis, the 

 centre (Budge's genito-spinal centre) lies at the 4th lumbar vertebra (rabbit) ; the 

 motor fibres of the vas deferens arise from the 4th and 5th lumbar nerves, which 

 pass into the sympathetic, and from thence to the vas deferens. The motor fibres 

 for the bulbo-cavernosus muscle, which ejects the semen from the bulb of the 

 urethra, lie in the 3rd and 4th sacral nerves (perineal). 



6. The parturition centre lies at the 1st and 2nd lumbar vertebras ( 453) ; the 

 afferent fibres come from the uterine plexus, to which also the motor fibres proceed 

 (Kdrner). Goltz and Freusberg observed that a bitch became pregnant after its 

 spinal cord was divided at the 1st lumbar vertebra. 



7. Vaso-motor Centres. Both vasomotor and vaso-dilator centres are dis- 

 tributed throughout the whole spinal axis. To them belongs the centre for the 

 spleen, which in the dog is opposite the 1st to 4th cervical vertebras (Bulgak). They 

 can be excited reflexly, but they are also controlled by the dominating centre in 

 the medulla oblongata ( 371). Psychical disturbance (cerebrum) influences them 

 ( 377). 



[8. Perhaps there are vaso-dilator centres ( 372).] 



9. The sweat centre is perhaps distributed similarly to the vaso-motor centre 

 ( 288). 



The reflex movements discharged from these centres are orderly co-ordinated reflexes, and 

 may thus l>e compared to the orderly reflexes of the trunk and extremities. 



Muscle Tonus. Formerly automatic functions were ascribed to the spinal cord, one of these 

 being that it caused a moderate active tension of the muscles a condition that was termed 

 muscle tow, or tonus. The existence of tonus in a striped muscle was thought to be proved by 

 the fact that, when such a muscle was divided, its ends retracted. This is due merely to the 

 fact that all the muscles are stretched slightly beyond their normal length ( 301). Even 

 paralysed muscles, which have lost their muscular tone, show the same phenomenon. 

 Formerly, the stronger contraction of certain muscles, after paralysis of their antagonists, and 

 the retraction of the facial muscles to the sound side, after paralysis of the facial nerve, were 



