Each language, an instantiation of LC, consists of a generative procedure that yields a discrete infinity of hierarchically structured expressions with semantic interpretations, hence a kind of “language of thought” (LOT), along with an operation of externalization (EXT) to some sensory-motor system, typically sound.
Here Chomsky draws a distinction between the Language Capacity (some capacity of the brain which enables humans and no other species to have the ability to learn and use a human language) and human language itself.
He is also saying that the language capacity is somehow integrated into the systems that create thoughts since we think in language.
And it is integrated into the sensory motor system which allows us to make the sounds associated with language. It also has to be integrated into the auditory system since we can understand the language we hear. And the visual system since deaf humans can understand the language they see.
The LC is what a single mutation in a single individual caused. The integration could have taken time and be varied between individuals. We already know that some people have better memory systems than others.
The integration can be altered, especially the ability to coordinate the mouth and tongue to make distinctive but arbitrary sounds. This can improve in time.
But the Language Capacity has not changed in tens of thousands of years.