Journal of morphology . re the medullary foldsare so abruptly bent downwards. Fig. 3. Older stage showing the beginning of the infolding to form the in-fundibulum and the optic vesicles. The tongue-like process (T) is separated bythis infolding from the anterior tip of the head (T). At op., the beginning of theoptic vesicles is indicated ; x, one of the two posterior eminences marking theposterior limit of the cephalic plate. Fig. 4. A still older stage showing the point mentioned for the previous also shows the concentric elevations (i, 2, 3) mentioned in the text. Fig. 5. Stage in
Journal of morphology . re the medullary foldsare so abruptly bent downwards. Fig. 3. Older stage showing the beginning of the infolding to form the in-fundibulum and the optic vesicles. The tongue-like process (T) is separated bythis infolding from the anterior tip of the head (T). At op., the beginning of theoptic vesicles is indicated ; x, one of the two posterior eminences marking theposterior limit of the cephalic plate. Fig. 4. A still older stage showing the point mentioned for the previous also shows the concentric elevations (i, 2, 3) mentioned in the text. Fig. 5. Stage in which the medullary folds have begun to rise. The frontalflexure is considerably advanced. At op are shown the external elevations of theoptic vesicles. Fig. 6. Embryo viewed from such a position as to show the optic vesiclesexternally {op) and internally {op). The tongue-like process is bent downwardsand backwards in the median plane, and is hidden from view by an edge of thehead-folds. Journal of Morphology VolM. ?« K .ri. <. cx^ SOME NERVE-MUSCLE EXPERIMENTS ON THEFROG {Rana Catesbiand)} HOWARD AYERS. The experiments herein recorded have to do with the in-fluence of the rate of stimulation upon the propagation of theresults of electrical stimuli in peripheral nerves. This topichas been the subject of recent investigations by several physi-ologists, among whom are Dr. F. H. Hooper ^ and N. Weden-sky,^ who, as a result of their researches, consider the rate ofstiniidation to be as important a factor affecting the propaga-tion of nerve force as the intensity of the stimulus is con-ceded to be, I shall first describe the experiment on thefrogs larynx, then those on the antagonistic muscles of theleg of the animal. For an account of the physiology of the mammalian larynxthe reader is referred to Dr. Hoopers excellent resume inthe above mentioned paper (i) where the experimental resultsof all the studies of this structure — reaching back somecenturies — are recorded.
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