GENERAL CUTANEOUS SNBDIVISION. Ill 



in the dorsal horn. While the collaterals make connections 

 which serve for relatively simple and direct reflexes, the connections 

 by v^^ay of the dorsal horn serve for complex reactions and for 

 sensation. 



The structure of the dorsal horn and its secondary connections 

 are best understood in the region at the junction of the spinal 

 cord and brain where the dorsal tracts of the cord have their 

 ending and where a part of the cutaneous fibers of the head also 



Fig. 53. — Some cells in the dorsal horn of the chick embryo of five days. From 

 Cajal (Textura, etc.)- A, dorsal root; B, transverse cell of the substance of Rolando; 

 C, cell of the substance of Rolando; D, cell of the posterior horn whose neurite 

 goes to the dorsal commissure; E, interstitial cell v^^hose neurite goes to the dorsal 

 commissure; F, dorsal commissure. 



end. In this region the dorsal horn is considerably enlarged in 

 all vertebrates and in man it forms the two large nuclei of the dorsal 

 funiculi. In lower vertebrates there is a single large nucleus of 

 the dorsal funiculus. This nucleus consists of large and small 

 nerve cells imbedded in a \ery rich and intricate interlacing of 

 their own dendritic branches and of the end-branches of cutaneous 

 nerve fibers. The small cells have relatively short and simple 

 dendrites and send their neurites among the cells of the dorsal 



