The whitish mass of soft matter (the center of the nervous
   system, and the seat of consciousness and volition) which is inclosed
   in the cartilaginous or bony cranium of vertebrate animals. It is
   simply the anterior termination of the spinal cord, and is developed
   from three embryonic vesicles, whose cavities are connected with the
   central canal of the cord; the cavities of the vesicles become the
   central cavities, or ventricles, and the walls thicken unequally and
   become the three segments, the fore-, mid-, and hind-brain.