376 C. JUDSON HERRICK 



The tractus spino-tectalis, after separation from the tractus 

 spmo-bulbaris and tractus spino-cerebellaris (fig. 7, tr.sp.t.) 

 crosses from the lateral to the medial side of the tractus spino- 

 cerebellaris, takes up its position medially of the bulbar lemniscus 

 (Im.) and then ascends into the tectum mesencephali (figs. 4 to 6). 

 It can be followed as several small compact bundles of fibers 

 throughout the length of the midbrain, and here most of its fibers 

 end by free arborizations which spread widely through the lateral 

 part of the tectum. Some of these fibers, however, continue 

 farther forward to end in the thalamus. 



The fibers of the spino-bulbar, spino-cerebellar, spino-tectal 

 and spino-thalamic tracts appear to form a single system of closely 

 related elements. They are only incompletely separated even in 

 the rostral end of the oblongata under the cerebellum, and collat- 

 erals of the spino-tectalis fibers have in several cases been seen 

 to enter the cerebellum (figs. 19 and 47). 



Summary. The secondary sensory tracts of the oblongata of 

 larval Amblystoma may be summarized as follows : The neurones 

 of the second order in the sensory region are generally related to 

 two jpr more different roots, so that few of the secondary tract 

 fibers conduct sensory impulses derived from a single type of 

 peripheral sense organ. Nevertheless the chief tracts are compar- 

 able in a general way with the corresponding tracts of mammals 

 and probably each has a single dominant physiological function. 



There are reflex connections between the sensory centers and 

 the motor nuclei of the oblongata and cord, but the details of 

 these pathways have not been determined. The ascending 

 secondary tracts are more clearly defined. There is an important 

 ascending system in the dorso-lateral fasciculus of the spinal 

 cord which ends in the caudal end of the oblongata, and a second 

 system farther ventrally which extends the entire length of the 

 brain stem as far forward as the thalamus. This spinal lemniscus 

 contributes fibers to the motor centers of the oblongata (tractus 

 spino-bulbaris) , to the eminentia trigemini (tractus spino-bulbaris 

 trigemini), to the cerebellum (tractus spino-cerebellaris), to the 

 midbrain (tractus spino-tectalis), and to the thalamus (tractus 

 spino-thalamicus). From the area acustico-lateralis of the oblon- 



