What is the proper position of the erector spinae muscles situated from medially to laterally relative to the axis of the vertebral column?

These group of muscles called erector spinae muscles arises from a tendon in the sacral area and pelvis, it extends up to the occipital bone.

Erector spinae muscles originates from the SPINOUS PROCESSES of T9-T12 of the thoracic vertebrae and inserts into the SPINOUS PROCESSES of T1-T2 of the cervical vertebrae

They therefore run vertically on either side of the spine (medially and laterally).

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.