The foregoing groupings have been made out almost entirely from cases of adult spinal paralysis or else of lead palsy. In the lower extremity it is much more difficult to establish such definite muscular association. Certain laws, however, can be made out: 1st. The liability to paralysis increases from the thigh toward the foot; thus, the muscles moving the thigh on the pelvis are the least liable to paralysis, then those moving the leg on the thigh, while the muscles moving the foot and leg and thigh are the most frequently paralyzed of any in the body. 2d. Of the upper thigh-muscles, the glutæi are not infrequently paralyzed, the ilio-psoas hardly ever, the adductors rarely except in total paralysis. 3d. Of the muscles moving the leg on the thigh, the quadriceps extensor is very frequently paralyzed—the most often, indeed, after the foot-muscles: the sartorius is almost always exempt; the liability of the hamstring muscles corresponds to that of the thigh adductors. 4th. At the foot the tibialis anticus often suffers from isolated paralysis, sharing in this respect the fate of the deltoid in the upper extremity—a fact already noticed by Duchenne. On the other hand, (5th) the tibialis anticus often remains intact while the other muscles supplied by the perineal nerve, the perineus longus and brevis, are completely paralyzed.46
46 Thus Buzzard relates a case of paralysis involving the quadriceps extensor and peroneal muscles, while the anterior tibial were intact.
The remarkable contrast in the morbid susceptibility of the quadriceps on the one hand, and the sartorius on the other, suggests dissociations of their nuclei. Remak relates one interesting case (Obs. 13) where the sartorius was paralyzed—coincidently with the quadriceps, it is true, but also with partial paralysis of the ilio-psoas muscle, which is as rarely attacked as the sartorius itself. The two facts, taken together, would indicate that the nucleus of the sartorius lies high in the lumbar enlargement, in proximity to that of the ileo-psoas. The inference, continues Remak, is reinforced by functional considerations, since the sartorius, obliquely flexing the leg on the thigh, is generally in action at the moment that the psoas flexes the thigh on the pelvis.
Again: according to Remak the tibialis anticus is generally paralyzed together with the quadriceps extensor, although supplied by a different nerve.47 And this should be expected from the necessity of exciting dorsal flexion of the foot by means of the tibialis anticus at the moment of extending the leg for the act of walking.48
47 Obs. 14, 15, 16, 17, from Remak's essay.
48 At the moment that the foot is thus flexed, however, to allow the leg to be swung forward, the thigh and leg are both slightly flexed.
Ferrier, from his experiments on the roots of the lumbar plexus, is inclined to doubt this association of the tibialis anticus with the quadriceps, and he adduces Buzzard's case, already quoted, to show coincident paralysis of the quadriceps and peroneal muscles. It is not improbable, however, that fibres associated together in nerve-roots may again diverge in the cord, and thus the discrepancy would be explained.
DIAGNOSIS OF SPECIAL PARALYSIS.—Paralysis of isolated muscles may sometimes be concealed by the vicarious action of their synergists: thus of the extensor communis for the tibialis anticus. Paralysis of both legs and feet may even be partly concealed by the energy of the thigh-muscles, which, using the paralyzed segments of the limbs as inert supports, succeeds in effecting locomotion.49 On the other hand, in limbs apparently abandoned to total paralysis persevering search will often discover some muscles or parts of muscles which respond to faradic electricity: these must be considered as susceptible of ultimate recovery.
49 Thus in Cornil's famous case, Soc Biol., 1863.
The following table sums up some special diagnostic marks for the different paralyses50 afforded by the position of the limb and loss of movements: