348 C. JUDSON HERRICK 



figures show no such dendrites crossing in the ventral commis- 

 sure in Salamandra. 



So far as appears from previous descriptions and from my own 

 observations there is Uttle evidence of any great capacity for 

 functional localization in the spinal cord of these larvae beyond 

 the general distinction between dorsal sensory and ventral motor 

 regions. The anatomical arrangement suggests that in the 

 normal functioning of the spinal cord, so far as concerns the larger 

 neurones at least, any stimulus whatever discharging into the 

 dendritic complex of the cord, whether derived from the dorsal 

 roots or from any of the longitudinal fiber tracts of the white 

 substance, would naturally call forth a total reaction of the entire 

 body musculature such as the typical swimming reaction. 



The earliest reflexes to appear in the spinal cords of these larvae 

 have been shown by Coghill ('09) to be crossed reactions involving 

 an ascending impulse in the dorsal tracts, a decussation in the 

 ventral commissure of the upper levels of the cord or in the oblon- 

 gata and a descending impulse in the ventro-lateral fiber tract of 

 the opposite side. But in the half grown larvae here under con- 

 sideration there is evidently present in addition to this primary 

 connection a very complete mechanism for purely local reflexes 

 within a single segment, including a direct synaptic connection of 

 dorsal root fibers with dendrites of ventral horn cells of the same 

 side, as well as an intricate system of intrinsic correlation neu- 

 rones in each segment for local and remote reactions. 



THE GENERAL STRUCTURE OF THE MEDULLA OBLONGATA 



As the spinal cord passes over into the medulla oblongata the 

 fundamental histological structure remains essentially similar, 

 but there are important differences in the details of the functional 

 connections of the constituent neurones. The sensory fibers of 

 the roots of the cranial nerves which enter the oblongata are segre- 

 gated into distinct functional systems, whose peripheral connec- 

 tions have been accurately determined by Coghill ('02). The 

 root fibers of these functional systems as they enter the oblongata 

 give to the white substance of the receptor region a definite pattern 

 and the great ascending and descending correlation tracts simi- 



