I think Language & Myth is the place to start, but I can't remember. I've got it at home.
As I remember L&M is rather vague and doesn't develop the idea. It just outlines the basic idea that the origin o language originates in the realm of mythic thought as it generates the underlying connections between thought, language snd the world.
In turn mythic thinking finds its orgins in the emotive affect of the mind. I think you have to supply more recent thought here to make the learning inputs on the emotive affect is in the realm of the social, where all these come together as a primate and early human social systems.
Cassirer wrote several short works to introduce some of his ideas while he was writing the Philosophy of Symbolic Forms.
CG
(at work on break)