Abstract
Abstract (1) Experiments were carried out on several species of vertebrates to extend knowledge of spino-bulbo-spinal (SBS) and propriospinal reflexes. (2) Vertebrates studied included the following. Mammals: kangaroo rat, bat, sloth, dolphin, wallaroo, opossum, sheep, seal and mangabey. Birds: chicken, pigeon and parrakeet. Reptiles: snake, alligator, caiman, iguana, lizard, horned lizard, chameleon and turtle. Amphibians: frog, toad, newt and mud puppy. Fish: halibut and the horn shark. All experiments, except that on the dolphin, were performed under chloralose anesthesia. Electrical stimulation was applied to the dorsal roots of sensory nerves in a fore- or hindlimb, and electrical responses were recorded from motor nerves and muscles in any of the extremities. Decerebration and spinal transection were performed for analysis of suprasegmental controls. (3) Identification of SBS reflexes in various species was based on similarities to SBS reflexes in the cat 7 . SBS reflexes were obtained in all mammals and birds, and in the frog and toad. However, SBS reflexes were not observed in reptiles, amphibians (except frog and toad), shark and bony fish. (4) Interlimb reflexes involved both SBS and propriospinal reflexes in mammals, birds, frog and toad. In contrast, other vertebrates lacked the SBS reflex, having to depend on propriospinal reflexes for interlimb coordination. (5) Descending propriospinal reflexes from forelimb to hindlimb were obtained in all vertebrates except, understandably, the shark and snake. However, ascending interlimb reflexes from hindlimb to forelimb were observed in mammals, birds, frogs, toads and turtles. The turtle exhibited a strong criss-crossed forward interlimb reflex. Tailed animals, including birds, exhibited some interesting aspects of longitudinal reflex control. (6) A comparative approach to the reflex mechanisms of the spinal cord and brain stem may provide useful alternative approaches for interpreting evolution.
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