Question

the ________ extends through the hindbrain, midbrain, and forebrain.

Answer 1

I believe the answer to this is Skull. 

Answer 2

Reticular formation extends from forebrain through midbrain till hindbrain.

Explanation:

The reticular formation comprises of neuron which forms a complex set of network which extended from midbrain and hindbrain. This plays an important role in sleep and motor activity. There are two pathways in reticular formation which includes ascending and descending reticular formation. The ascending pathway is connected with cortex and descending pathway is connected with spinal cord.  

There are three columns in reticular formation which are median, medial zone, and lateral zone.