16 A lucunstnaiioii of llic Nuclear Masses in 



from dorsal view shows as a rather smooth, narrow cohmm in close relation 

 to the dorsal fissure. The nucleus in its caudal portions has a poorly defined 

 mesial surface and the nuclear material extends practically to the dorsal 

 fissure, even though the main characteristic nuclear mass, on superficial 

 inspection, seems to end at some distance lateral to the furrow. Hence, on 

 reconstruction, the nuclear columns of both sides, representing the two 

 nuclei, lie in fairly close approximation in the mid-dorsal line. This mesial 

 dorsal edge of the two nuclei shows considerable curving, a phenomenon due 

 to the peculiarities in the nuclear formation, as the dorsal longitudinal fissure 

 was reconstructed as a straight line and served as one of the main guides 

 against lateral deviation. At a level with the caudal extremity of the nucleus 

 fasciculi cuneati, the dorsal surface of the nucleus fasciculi gracilis shows 

 three dorsal spurs (figures 3 and 9). The most lateral of these, bounded 

 mesially b}^ a deep furrow, is short and rather thin, exhibiting a tendency 

 to fold in a gentle curve toward the mid-line. The middle of the spurs 

 projects dorsally more strikingly than does the lateral, as shown in figure 2. 

 This middle spur arises gently from the dorsal portion of the nucleus caudal 

 to the inferior end of the cvnieate cell-mass and only slowly assumes the 

 character of a sharp spur. At its cephalic end it curves rather abruptly 

 mesially and loses its character in a broader mesial slope. The mesial of 

 these caudal dorsal spurs is very poorly defined, being constituted of a 

 series of imperfectly differentiated notches, as shown in figure 3. This mesial 

 spur can be traced cephalad somewhat further than the other two; it ends 

 in a small rounded knob of nuclear material. The ]ioints of cephalic termi- 

 nation of these three spurs constitute a fairly straight line, which runs from 

 the lateral spur mesially and cephalad. The lateral of these spurs, after 

 ending, may be considered to begin a short distance cephalad to its termina- 

 tion, as a fairly well-defined ridge which continues ui)ward to end in bulbous 

 dilatation over the broader cephalic half of the nucleus. Lateral to the 

 superior portion of this ridge is a deep furrow, on the outer side of which is 

 a small dorsal spur. The middle of the inferior group of dorsal spurs, after 

 a slight interruiition, is continued cephalad as a small, pyramidal projection 

 which ends at about the same level with the lateral spur. Mesially the third 

 spur is not made out. In the corresponding place, however, at the point of 

 cephalic termination of the other spurs, occur two small knob-like projec- 

 tions, both mesial to tlie middle spur. 



In the middle of these upi)er dorsal corrugations, the nucleus fasciculi 

 gracilis widens out rather abruptly. Above their cei)lialic terminations, 

 occurs a slight transverse depression, cephalic to which the nucleus presents 

 a smooth dorsal surface. It widens very slowly in its superior half, to reach 

 its greatest transverse diameter at a level with the calamus scriptorius. 

 Here the nucleus shows as a marked and prominent mesial shoulder, corre- 

 sponding to the widening out of the spinal canal into the fourth ventricle 

 (figure 3). Above this point the mesial dorsal edge of the nucleus rapidly 



