616 



PHYSIOLOGY OF THE BRAIN-STEM 



point somewhat farther back gave contraction of the pupil (cf. Fig. 230). 

 Stimulation at the anterior border of the aqueduct of Sylvius gave contraction 

 of the internal rectus, and stimulation somewhat farther back gave in serial 

 order contraction of the superior rectus, levator palpebrae superioris, inferior 

 rectus, and finally of the inferior oblique. When the stimulus was applied 

 to the lateral surface or the deeper parts of the corpora quadrigemina, or to 

 the cut surface of the transverse section in the optic thalamus, the pupil 

 became dilated. 



Bernheimer employed a similar method on monkeys. The two halves of 

 the oculo motor nucleus were separated by a median sagittal section and weak 



electrical stimuli were applied 

 at different points. The results 

 were isolated movements of 

 the different eye muscles inner- 

 vated from the side stimulated 

 and contraction of the pupil on 

 the side stimulated. The lat- 

 ter effect was obtained only 

 when the stimulus was applied 

 somewhat internal to the me- 

 dian cut surface below the 

 aqueduct and in the anterior 

 third of the region occupied 

 by the anterior quadrigeminal 

 body i. e., in the region of the 

 small-celled median nucleus 

 (Ke M, Fig. 272). 



Special observations as to the 

 connections of the two sides of 

 the oculo motor nucleus afford 

 some grounds for believing 1 that 

 the nuclei of the two sphincters 

 (pupil and accommodation) as 

 well as the nuclei of those ex- 

 trinsic muscles which take part 

 in synergic movements of the 

 eyes, are united. The latter is 

 shown by the fact that synergic 



movements cease when the paired nuclear region is split in two by a median 



sagittal section. 



Complete division of the brain at the anterior end of the midbrain pro- 

 duces a remarkable state of inertness in the muscles, which is described by 

 Sherrington under the name of acerebral rigidity. It is recognized by the 

 fact that certain muscles become stiff; the elbows and knees, for example, 

 are rigidly extended, the tail is inflexible, etc. This condition appears to be 

 due to the influence of the afferent nerves from the regions affected, for the 

 stiffness in the arm muscles, for example, entirely disappears after section 

 of the posterior roots for the arm. 



FIG. 273. Schematic representation of the nucleus of 

 oculo motor nerves, after Bernheimer. The red lines 

 indicate the direct, and the black the crossed root 

 fibers. B.M., intrinsic muscles of the eye; Lev., 

 levator palpebrae sup. ; R.s., superior rectus; R.int., 

 internal rectus; Obl.inf., inferior obliquus; R.inf., 

 inferior rectus; Tr., superior oblique. 



