The prominent bony ridge that you can palpate across the posterior surface of the scapula is the

Spine.

Explanation:

The spine is the most prominent feature of the posterior scapula. It runs transversely across the scapula, dividing the surface into two.

The spine of the scapula is a prominent plate of bone,it crosses obliquely the medial four-fifths of the scapula at its upper part, and separates the supra- from the infraspinatous fossa.

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.