346 Journal of Comparathe Neurology and Psychology. 



The li.i^lit area ventral to the lateral tip of the substantia 

 gelatinosa is present in the lumbar region, and corresponds to 

 the similar area of the higher levels. 



At the lumbar level the fasciculus gracilis does not appear 

 in the section, and the funiculi dorsales are depressed below the 

 level of the dorsal column on either side. 



In all levels of the spinal cord there is a large amount 

 of medullation, numerous well medullated fibers of all classes 

 being present. Throughout the gray substance everywhere 

 there are fibers passing in every direction, both large and small, 

 separate and grouped into heavy bundles. Commissural fibers 

 cross the median line on both sides of the canalis centralis, the most 

 conspicuous commissure being the anterior. Here fibers running 

 in the plane of the section are extreme!}- abundant. The\' pass 

 among man\' cross sections of fibers. Two bundles are enclosed 

 by these commissural fibers (fig. 3, plate V, v), and are to be 

 found in this position at all levels and in all individuals exam- 

 ined. 



Small bundles of fine fibers are seen pa-^sing longitudin- 

 ally at the junction of the cervix and caput of the dorsal col- 

 umn (fig. I, Plate V, X). The)' constitute a pirt of a very ex- 

 tensive reticular formation which in this region passes through 

 one-half or two-thirds of the cervix. The processus reticularis 

 is well marked in the lateral region o( the gray substance at 

 every level. 



1. In summarizing the appearances in the medulla spinalis 

 of the guinea pig at birth emphasis is to be laid upon (i) the 

 three partially medullated areas in the cervical and thoracic lev- 

 els, to be found (a) in the fasciculus gracilis, (b) at the ventral 

 border of the fasciculus cuneatus (the pyramidal tract), and (c) 

 at the ventral margin of the apex of the dorsal column ; (2) 

 the two partially medullated areas in the lumbar cord, (a) the 

 pyramidal tract which is less well marked than at higher levels, 

 and (b) the area ventro-lateral to the substantia gelatinosa. 

 The fasciculus gracilis is not present in the lumbar cord. 



2. In transverse sections the perifjheral third of the white 

 substance does not appear to contain so many medullated fibers 



{ 54] 



