8 1 4 THE SPINAL CORD. 



of muscles are more readily accessible to reflex stimuli than are others. 

 The flexors of the knee and hip and ankle are more accessible than the 

 extensors, and especially than the abductors of the digits. In the fore- 

 limb the adductors and the retractors of the upper-limb are the more 

 accessible. The readiness with which reflexes can be elicited varies 

 also with the region of the skin. As judged by pathic stimuli, e.g. by 

 bits of paper soaked in acidulated water, the order of efficiency in 

 descending scale runs in the frog somewhat as follows : anal region, first 

 and second digits, plantar and dorsum pedis, outer side of knee, mesial 

 half of dorsal aspect of lower half of leg, rest of leg except calf, outer 

 side of thigh, upper half of calf, mesial side of ventral aspect of thigh, 

 popliteal region. 



The reflex of extension of the frog's hind-limbs is said to lie farther tail- 

 ward than that of flexion. Gad * found that after transection behind the eighth 

 pair of spinal roots, i.e. behind the second of the three constituting the hind- 

 limb plexus, all the conditions for the reflex of extension of the limb obtain. 

 Sirotinin 2 found the levels of maximum spinal excitability of the ilio-psoas 

 semitendinosus and gastrocnemius to lie in the frog opposite respectively the 

 fourth, fifth, and sixth vertebrae, both for mechanical and electrical stimuli. It 

 is not clear, however, that the contractions he studied were always reflexly 

 produced. 



In the bird (pigeon) the post-thoracic spinal cord after isolation con- 

 summates various reflexes employing the musculature of the legs. The 

 muscles are not toneless, but on the contrary tense. Contact with 

 straw in the cage often suffices to excite wild "struggling" of the legs. 3 

 If one of the dependent feet be, when the bird is lifted, pressed, it is 

 drawn up, and the opposite leg is extended. If the extended leg is then 

 gently passively flexed, extension of the contra-lateral, previously flexed, 

 ensues. Not unfrequently, when the animal is lifted by the shoulders, 

 alternate flexion and extension of the hind-limbs is started which may last 

 more than a minute, flexion and extension alternating about twice a 

 second. The tail feathers are immediately spread when the position of the 

 bird, as held comfortably in the hand, is such that its head lies abnormally 

 high, or the plane of the back is at greater inclination 4 to the horizon 

 than in its ordinary erect posture. 5 Singer could not obtain inhibition 

 of these reflexes by strong or pathic stimuli, as Goltz found possible in 

 the dog. 



In the mammal similar studies have been made. Evacuation of faeces 

 and urine ensue on rectal or vulval stimulation. Even with complete 

 absence of the corresponding region of the spinal cord, these evacua- 

 tions are more or less regularly maintained, the contents of the viscera 

 exciting efficient contractions of the visceral muscles. The contractions 

 when the cord is present can he reflexly inhibited by strong cutaneous 

 stimuli. Wagging movements of the tail can be elicited by stimuli to its 

 skin. The musculature of the paralytic limbs is far from toneless. 

 When the spinal transection lies in the lower thoracic region, the 



1 Verhandl. d. phys.-mcd. Gesellsch. in Wiirzburg, 1884, Bd. xviii. S. 8. Masius and 

 Vanlair seem to have found section through the 8th root practically destroy the spinal 

 reflexes for the parts of the limb not innervated from the 7th. But their account is 

 difficult to follow ; Mem. couron. Acad. roy. de med. dc Belg., Bruxelles, 1869. 



2 Arch./. Physiol., Leipzig, 1887, S. 154. 

 3 Schiff, "Lehrbuchd. Physiol.," 1858, S. 196. 



4 Singer, Sitzungsb. d. k. Akad. d. Wisscnsch., Wien, 1884, Bd. lxxxix. 



5 Goltz and Ewald, Arch./, d. ges. Physiol., Bonn, 1896, Bd. lxiii. 



