Automatic activity of the locomotor centres of the lumbar cord in lizards.

My previous experiments with salamanders {Triton cristatus; ten Cate, 1927) and tortoises (Testudo graeca; ten Cate, 1937) have shown that, after transection of the spinal cord in the thoracic region, locomotor movements of the hind limbs can be observed under favourable conditions while the front limbs remain motionless. These alternating movements are well co-ordinated but last only a short time; the front limbs then also begin to move. To confirm these observations, made by chance, experiments were performed by a new method in which, after severing the thoracic cord in the lizards Lacerta lepida and L. viridis, the locomotor movements of the hind limbs could be studied after the front limbs had been immobilized. In decapitated lizards (L. viridis) Steiner (1886) made 'slices' of the body using sharp scissors, starting at the front and working backwards. When he reached the hind part of the body he observed movements of the hind limbs and of the tail which resembled locomotor movements. These locomotor movements, which lasted a short time, were provoked by the violent excitation of the spinal cord as a result of the transection. Similar alternating movements of the hind limbs were described by Graham Brown (1916) in spinal cats and by Tarchanoff (1895) in spinal ducks. The literature indicates, and I have been able to convince myself repeatedly, that in quadruped animals during progression the alternating movements of the hind limbs are closely integrated with the locomotor movements of the front limbs. This was first shown by Sherrington (1914) in spinal cats and by Gray & Lissmann (1940, 1947) in toads. It is also well known that animals with a transected thoracic cord usually show locomotor movements of the hind limbs when they walk forward with their front limbs. In animals with an isolated lumbar cord the occurrence of walking movements in the hind limbs requires a certain degree of stretching of these limbs, which is caused by the locomotor movements of the front limbs. By stretching the limbs proprioceptors and exteroceptors become stimulated and alternating walking movements are then induced by reflex action. The rhythm of the front limbs is taken up by the hind limbs. To establish that the isolated lumbar cord can elicit walking movements completely autonomously it is necessary to eliminate the movements of the front limbs.