MEDULLA OBLONGATA 163 



first group. There is some evidence of a separate trigeminal lemnis- 

 cus, as described below. 



1. THE SPINAL LEMNISCUS (fIGS. 3, 9, 10, 11, Im.Sp.) 



The spinal lemniscus is an extensive system of fibers ascending 

 from the spinal cord and here lying immediately ventrally of the 

 spinal V root. In the cord these fibers arise as axons of cells of the 

 dorsal gray column, which decussate in the ventral commissure. In 

 the region of the calamus this tract receives extensive additions from 

 the nucleus funiculi, the spinal V nucleus, and the commissural 

 nucleus of the opposite side (figs. 3, 87). Some of these crossed fibers 

 from the calamus region have thinner collaterals, which descend for 

 a short distance in the ventral funiculus of the spinal cord. The 

 ascending fibers, at first, lie in the ventral funiculus (figs. 41, 42) 

 but soon turn dorsally to join those from lower levels of the cord 

 ('446, figs. 9-11). The most lateral and ventral fibers of this mixed 

 bundle terminate in the reticular formation of the medulla oblongata 

 — tr. spino-bulbaris (figs. 3, 88, 89, 90). The others at the level of the 

 V nerve roots separate into spino-cerebellar and spino-tectal tracts. 

 Many of the spino-cerebellar fibers are collaterals of the spino-tectal 

 fibers (fig. 10; '14a, p. 376). Some fibers of the spino-tectal tract 

 continue past the midbrain to end in the dorsal thalamus (fig. 34). 

 The entire course of this complex is shown in a diagram ('396, fig. 26) 

 drawn from three adjoining sagittal sections of a larva, and this is 

 confirmed by elective Golgi impregnations of the adult. Terminals of 

 this tract in the dorsal thalamus are seen in figure 44. 



2, THE GENERAL BULBAR LEMNISCUS (hn.) 



This large fascicle, the general bulbar lemniscus, receives fibers 

 from all parts of the sensory zone of the medulla oblongata (figs. 9, 

 11). These decussate in the ventral commissure and ascend medially 

 of the reticular formation (figs. 89, 90). In the isthmus they turn 

 dorsally and traverse the midbrain ventrally of the tectal formation, 

 some fibers continuing forward into the dorsal thalamus (figs. 27-34, 

 91-94). These fibers may apparently carry nervous impulses acti- 

 vated by all kinds of sensory fibers which enter the medulla oblon- 

 gata. Their terminals are spread quite uniformly throughout the 

 entire extent of the tectum, and here they mingle with those of the 

 spinal lemniscus (fig. 11; '396, fig. 96). There is little evidence of 

 physiological specificity in either of these tracts, save that one comes 

 from the spinal cord and the other from the medulla oblongata and 



