Risus

(ri'-zus) [L.]. A grin or laugh. R. sardonicus, the sardonic grin, a peculiar grinning distortion of the face produced by spasm of the muscles about the mouth, seen in tetanus.

Ritter's Disease. Dermatitis exfoliativa of the newborn. R.'s Fiber, a delicate fiber regarded as a nerve-fiber, seen in the axis of a retinal rod, near the peripheral end of which it forms a small enlargement. R.'s Law of Contraction, stimulation of a nerve occurs both at the moment of closing and of opening of the electric current. R.'s Tetanus, tetanic contractions occurring on the opening of the constant current which has been made to pass for some time through a long section of a nerve. In man the phenomenon does not occur under physiologic conditions, but it is seen in tetany.

Ritter-Rollet's Phenomenon. Flexion of the RITTER-VALLI'S LAW 840 ROLANDO'S ARCIFORM FIBERS foot following the application of a mild gal- vanic current, and extension following that of a strong current.

Ritter-Valli's Law. Section of a living nerve is followed by a gradual loss of irritability, preceded by a slight increase, the phenomenon taking place centrifugally from the divided end.

Riverius' Draft. A solution of sodium citrate.

Rivinian Canals, R. Ducts. The ducts of the sublingual gland. R. Foramen. See Bochdalek's Canal. R. Glands, the sublin- gual glands. R. Ligament. See ShrapnelVs Membrane. R. Notch, R. Segment, a notch of irregular outline at the upper border of the sulcus tympanicus; it is marked at each end by a small spine.

Rivolta's Disease. Actinomycosis.

 

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