What is the meaning of うち in this sentence?


I read the definition of 本能:

> ほん-のう [1][0] 本能 （１）生まれつきもっている性質や能力。特に，性質や能力の **うち** ，非理性的で感覚的なものをいう。

I understand the 生まれつきもっている性質や能力 part as "Qualities and abilities" x holds
naturally. But I don't understand the second part, especially the function of
うち there. This is not the same thing as うちに so I am not sure.

