609 
1907-8.] Middle Cells of Grey Matter of Spinal Cord. 
the segment, with the disappearance of the median motor group, the middle 
cells extend forwards almost to the antero-internal angle of the anterior 
horn, and may be very abundant in the anterior area. 
S 2. — Area of distribution proportionately larger than in S 1, extending 
further forwards and relatively further outwards in the anterior horn. 
Although individual sections may be picked out with few cells, they are 
on the whole very numerous. Vary much in size. Scattered diffusely or 
forming loose groups in almost any part, but anterior, central, and reticular 
Fig. 10. 
S 4—210 L ( x 33 ). 
a. Anterior median motor group. 
b. Small round cells in posterior part of reticular formation, appar- 
ently the representatives of the sacral intermedio-lateral tract. 
The middle cells occur as fairly large cells over the whole of the 
anterior horn except where group a is ; also in the central and post- 
central areas and area of Clarke’s column. In the reticular area they 
are mingled with group b. 
are perhaps the most common. Have much the same variations in size and 
irregularity of occurrence in all areas. 
S 3. — Area of distribution as in S 2. Cells diminishing in number in 
lower end, where they are only found thickly in the base of the anterior 
horn. Distinct groups are now rather rare ; at places they may be thickly 
scattered rather than grouped. 
S 4. — See fig. 10. — With the gradual dying out of the motor group, the 
middle cell area gradually comes to take in the whole anterior cornua, as 
vol. xxvm. 39 
