THE SPINAL ANIMAL. 817 



of the cutaneous afferents of spinal roots rather than of the peripheral nerve 

 trunks, furnishes evidence that there is still even in the most complex spinal 

 organ some segmental partition in the framework of its function. The 

 cutaneous and, where examined, muscular distribution of the afferent roots l 

 and the muscular distribution of the efferent roots is shown to be, even in the 

 limb regions, as certainly and obviously segmental as is their fascicular con- 

 nection with the spinal organ itself. The physiological architecture of even 

 the mammalian limb exhibits therefore a segmental plan. On the other hand, 

 the solidarity and homogeneity of the plurisegmental motor innervation of the 

 individual limb muscles and of the plurisegmental centripetal bond between 

 each practical unit of limb surface and spinal organ, warns against too lightly 

 inferring that an ancestral segmentation is still upheld in the existing 

 mechanisms of all the spinal regions of the vertebrate. 



THE SPINAL ANIMAL. 



When,instead of being tested in parts, the spinal cord is experimentally 

 examined as a whole, the reactions obtained are decidedly more complex. 2 



Amphioxus, after removal of its " head," on application of a stimulus, 

 still swims forward and right side up, though not with normal precision. 3 

 The decapitated eel swims well, turning, mounting, or diving, to normal 

 appearance. Its equilibrium is, however, impaired, 4 though when laid on 

 its back it rights itself. 5 The shark and ray still swim co-ordinately for- 

 ward after decapitation or bulbar transection,but equilibrium is impaired. 6 



The "spinal" frog still retains tonus in the skeletal musculature, 

 and can, it is said, spring. 7 It is doubtful whether "spontaneous" 

 movements, including respiratory, ever occur, even in animals kept 

 for months under observation. When undisturbed, the creature 

 sits with head abnormally low. The tonus of the muscles seems to 

 have suffered some diminution, though in many cases it is practically 

 impossible to obtain absolute assurance of this. During the period 

 of shock immediately succeeding transection, it is obvious enough, but 

 it is evanescent. The tonus of the extensors of the limbs seems to 

 be more depressed than that of the flexors, at least at hip and knee. 

 On an attempt to passively draw the limb into extension, the whole 

 animal may be pulled back without the limb being straightened. 

 Similarly with the limbs of Astacus after transection behind the 

 supra-oesophageal ganglion ; the paralytic appendages are more flexed 

 than normal at their " hip " joints, 8 and the tail-fan is less spread. In 

 the monkey, with thoracic transection I found that the hips and 

 knees become strongly and permanently flexed after the lapse of six 

 months. 9 In a dog, six months after cervical transection, I found the 

 ankles keep distinctly over-extended, but such rigidity is not the rule. 



1 Sherrington, Proc. Roy. Soc. London, 1892, vol. Hi. ; Phil. Trans., London, 1893. 



2 Space unfortunately does not allow here of even the briefest sketch of the study of the 

 reactions obtainable from the nerve-cord of Invertebrata. As contributory to a general 

 conception of the "spinal " animal, these are of utmost importance. For recent work refer- 

 ence can be made to papers by Bethe, Loeb, and others, chiefly in Arch. f. d. ges. PhysioL, 

 Bonn, 1891, Bd. xlix. and onwards, and to Loeb's " Einleitung in die vergleichende 

 Gehirnphysiologie," Leipzig, 1899. 



3 Danilewski, Arch. f. d. ges. PhysioL, Bonn, 1892, Bd. lii. 



4 A. Bickel, ibid., Bd. Ixviii. S. 111. 



5 W. Pfliiger, "Die sensor. Funcktionen d. Ruckenm.," Berlin, 1853, S. 18. 



6 Loeb, Arch. /. d. ges. PhysioL, Bonn, Bd. xlix.; Bethe, ibid., Bd. Ixxvi., in part 

 contra Steiner, op. ciL 



7 Pfluger, op. cit.; Schrader, Arch. f. d. ges. PhysioL, Bonn, 1887, Bd. xli. 



8 Bethe, op. cit. g Phil. Trans., London, 1897. 



VOL. II. 52 



