68 LABORATORY OUTLINE OF NEUROLOGY 



from their nuclei to cross ventrally of the ventricle to the other 

 side of the brain, thus forming the decussation of the lemniscus. 

 This tract after its decussation can be followed through the series 

 of sections as far as the thalamus. In the lower part of the 

 medulla oblongata these fibers will be found in the interolivary 

 space near the median plane (Herrick ('15), Figs. 64, 72, 73). 

 They are bounded ventrally by the cortico-spinal (pyramidal) 

 tract, and dorsally by the tecto-spinal tract. Dorsally of the 

 latter is the longitudinal medial fasciculus. At the level of the 

 pons the medial lemniscus begins to turn laterally and in the 

 midbrain it lies dorsally of the substantia nigra (Herrick ('15), 

 Fig. 75) . In sections through the midbrain and thalamus these 

 fibers can readily be followed forward to their termination in 

 the lateral nucleus of the thalamus (Herrick ('15), Figs. 77, 78, 

 and 79). The medial lemniscus carries general proprioceptive 

 nervous impulses from the spinal cord to the thalamus. 



Identify the medial lemniscus in the sections and draw it into 

 the outlines as far forward as the material provided will permit. 

 See, in addition to the figures cited in the previous paragraph, 

 Section 62 (1) to (11); Cunningham ('15), Fig. 579, p. 651; 

 Morris ('14), Fig. 632, p. 803; Villiger ('12), Figs. 154, 155, pp. 

 167, 168. Directions for the dissection of the medial lemniscus 

 of man will be found in Section 108. 



78. The spinal lemniscus. — The ascending secondary pathway 

 for exteroceptive sensibility (touch, temperature, pain) from 

 the trunk and limbs is the spinal lemniscus, or spino-thalamic 

 tracts. There are two of these tracts in the cord, the tractus 

 spino-thalamicus dorsalis for pain and temperature, and the 

 tractus spino-thalamicus ventralis for touch and pressure 

 (Herrick ('15), Fig. 63). In the medulla oblongata these ac- 

 company the ventral spino-cerebellar tract (Herrick ('15), Fig. 

 73) and in the midbrain they join the lateral lemniscus (Herrick 

 ('15), Fig. 75). 



It is difficult to demonstrate these tracts in either gross or 

 microscopic material. From your reference books learn their 

 courses and enter them in the outline drawings of the cross- 

 sections in their appropriate places. 



79. Summary of secondary general somatic sensory tracts. — 

 The general somatic sensory centers and tracts of the brain 



