The ornamental design for a handle portion of a dental syringe, as shown and described.
FIG. 1 is a perspective view of a handle portion of a dental syringe according to our new design;
FIG. 2 is a right side elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
Broken lines shown herein which are illustrative of environmental structure of the upper portion, buttons, tip, bottom opening, and neck circumference of the dental syringe form no part of the claimed design. Broken lines shown herein which define the upper bounds of the handle portion of the dental syringe form no part of the claimed design.