80 LABORATORY OUTLINE OF NEUROLOGY 



('18), Figs. 59 and 75.) These connections serve for reflexes of 

 more complex sorts than can be effected in the spinal cord alone, 

 in contrast with the lemniscus systems terminating in the 

 thalamus and thence connecting with the cerebral cortex, which 

 may serve conscious reactions. The spino-bulbar connections 

 are diffuse and are not readily seen in sections, though physio- 

 logically they are important. 



92. The longitudinal medial bundle. The fasciculus longi- 

 tudinalis medialis (the posterior longitudinal bundle) is an 

 important longitudinal motor co-ordination system which can 

 easily be followed in the microscopic sections through the 

 whole length of the midbrain and bulb and downward into the 

 fasciculus proprius of the cord. It is composed of heavily 

 myelinated fibers lying near the median plane immediately 

 ventrally of the ventricle. It has already been noted in con- 

 nection with the vestibular apparatus (Section 83). If its 

 entire course has not already been entered in the drawings, 

 this should be done now. It arises in front of the III nucleus 

 and is related with all of the motor nuclei of the brain and 

 spinal cord. It is used in conjugate movements of the eyeballs, 

 in vestibule-oculomotor equilibratory reactions, and in many 

 other reflex movements. See Barker ('01), Fig. 406, p. 617; 

 Bruce ('92), Plate XXVII, Fig. 1; Cunningham ('15), Fig. 

 524, p. 590; Piersol ('16), Fig. 965, p. 1117. 



93. Dissection of the longitudinal medial bundle. On the 

 right side of the divided sheep's brain this tract can be brought 

 to view by gentle scraping in the longitudinal direction on the 

 median cut surface immediately ventrally of the fourth ven- 

 tricle. In this way the fasciculus can be exposed throughout 

 the entire length of the brain stem. 



94. Microscopic study of the pyrami-dal tract. The tractu3 

 cortico-spinalis (fasciculus cerebro-spinalis of the B N A),OT 

 pyramidal tract, is the great descending voluntary motor path 

 between the motor areas of the cerebral cortex and the lower 

 motor centers. It can be readily identified in the sections 

 through the middle region of the medulla oblongata (see refer- 

 ences in Section 62), lying ventrally close to the median plane 

 below the olives. From the level of the olives follow it upward 

 also. Immediately below the pons it forms a sharp projection 



