SPINAL CORD AS A PATH OF CONDUCTION. 



177 



(touch, cold, heat) and protopathic sensibihty (cold, heat, pain), 

 see p. 274. The fibers oi these three general varieties are regrouped 

 in the cord in such a way that the epicritic and protopathic 

 temperature fibers are brought together into a common tract, 

 which is contralateral; the deep and cutaneous pain fibers are 

 likewise united into a common tract, which is contralateral, and 

 cutaneous pressure fibers, except those mediating tactile discrim- 

 ination, unite with the deep pressure fibers to form a common tract 

 which crosses the mid-line less promptly. This conception is 

 indicated in the accompanying schema (Fig. 79). According 

 to their interpretation, a complete unilateral lesion of the 

 cord in the cervical region would 

 be followed by a homolateral 

 loss of motion in the parts below, 

 and also of tactile discrimination 

 and muscle sense, using the latter 

 term to cover the deep sensibility in 

 regard to position and movements 

 of the limbs. On the contralateral 

 side there would be a loss of pain, 

 temperature, and pressure. 



The Descending (Efferent or 

 Motor) Paths in the Antero-lateral 

 Funiculi. — The main descending 

 path in the cord is the pyramidal 

 or cerebrospinal system of fibers. 

 In man, as shown in Fig. 75, there 

 are two fasciculi belonging to this 

 system — the anterior and the lat- 

 eral pyramidal tracts. Both tracts 

 arise from the anterior pyramids on 

 the ventral face of the medulla, 

 whence the name of the pyramidal 

 system. At the junction of the 

 medulla and cord the fibers of the 

 pyramids decussate in part, form- 

 ing a conspicuous feature of the 

 internal structure at this point, 

 known as the pyramidal decussa- 

 tion. According to the general 

 schema of this decussation (see Fig. 

 80), the larger number of the fibers 

 in the pyramid of one side pass 

 over to form the lateral pyramidal 

 fasciculus of the other side of the cord (4, 5), while a smaller part 

 (3) continues down on the same side to form the anterior pyra- 



Fig. 80. — Scliema representing 

 the course of the fibers of the pyra- 

 midal or cerebrospinal system: 1, 

 Fibers to tlie nuclei of the cranial 

 nerve; 2, uncrossed fibers to the 

 lateral pyramidal fasciculus; 3, fibers 

 to the anterior pyramidal fasciculus 

 crossing in the cord; 4 and 5, fibers 

 that cross in the pyramidal decussa- 

 tion to make the lateral pyramidal 

 fasciculus of the opposite side. 



