1042 



HUMAN ANATOMY. 



Section of spinal cord at level of sixth cervical segment ; anterior 

 cornua are very broad ; obliquely cut bundles of posterior root-fibres lie in 

 postero-lateral sulcus. Preparation by Professor Spiller. X 6. 



to higher levels by the ascending stem-fibres. Although the anterior reflex collat- 

 erals are, for the most part, in relation with the cells of the same side, it is probable 

 that some cross by way of the posterior commissure, and possibly also by the anterior 

 bridge, to the opposite ventral horn cells. It is doubtful, on the other hand, 

 whether either stem-fibres or collaterals of the posterior roots pass directly to the 

 anterior column either of tin- same or opposite sides (Zichenj. 



The root-fibres passing to the posterior horn include those which pene- 

 trate the substantia Rolandi, either as collaterals or stem-fibres of Burdach's or 



of Lissauer's tracts, to end 



FIG. 896. about the neurones within 



the Rolandic substance or 

 within the head of the pos- 

 terior horn. Their longitudi- 

 nal course within Burdach's 

 tract is ordinarily short ; 

 they then bend horizontally 

 and enter the gray matter 

 of the posterior horn, within 

 which they soon terminate 

 in end-arborizations around 

 the neurones of the II order. 

 Some fibres, however, do 

 not undergo T-division until 

 after entering the posterior 

 horn, where, within the Ro- 

 landic substance or caput 

 cornu, they then bifurcate, 

 in some cases the ascending 

 limbs pursuing a vertical course within the gray matter, particularly of the caput 

 cornu, for some distance before ending about the head-cells of the posterior horn. 



The tract of Lissauer, or marginal zone, situated immediately behind the 

 apex of the dorsal horn, receives the lateral group of the posterior root-fibres. These 

 are all of unusually small size and, after a short longitudinal course in which the 

 descending limbs predominate, they turn horizontally and, both as collaterals and 

 stem-fibres, penetrate the substantia Rolandi, about whose cells and those of the 

 caput cornu they end. 



From the foregoing description, it is evident that the dorsal root-fibres destined 

 for the posterior horn terminate in relation with neurones of the II order represented 

 chiefly by the cells of the substantia gelatinosa Rolandi, including the marginal cells, 

 and the inner cells of the caput cornu. 



The secondary or endogenous tracts of the posterior column arise as axones from the 

 neurones of the II order (the marginal cells, the cells of the substantia Rolandi and the head- 

 cells) situated within the posterior horn and include ascending and descending paths. 



The ascending secondary tract is composed of the axones derived from the posterior horn 

 cells of the same and, by way of the posterior commissure, opposite side, which pass into the 

 posterior column. Tn a general way, they occupy the ventral .field, although sharing it with 

 scattered strands of root-fibres and of descending endogenous fibres. The destination of the 

 fibres of this ventral tract is uncertain, some fibres pursuing a short and others a longer course 

 within the posterior column before entering the gray matter at higher levels to end in relation 

 with the posterior horn-cells, or, perhaps, in some cases, with the neurones within the nuclei of 

 the medulla (Rothmann). 



The descending secondary tracts, as shown by degenerations following lesions involving 

 the posterior column, occupy varying but fairly well differentiated areas. In the cervical and 

 upper thoracic con I the descending limbs of the long posterior fibres are collected into the 

 comma bundle of Schnltze, which extends along the median margin of Burdach's tract. In 

 the lower thoracic- and lumbar cord is formed an elongated half-ellipse along the posterior 

 median septum which, with the corresponding bundle of the opposite side, produces the oval 

 field of Flechsig. Still lower, in the sacral cord, fibres lie at the junction of the median septum 

 and the posterior surface of the cord as the medio-dorsal triangular bundle of Gombault and 

 Philippe. Additional descending endogenous fibres are scattered in the ventral field. It is 



