Triangle is an amplifier and rectangle is a black box (“don’t worry what’s in here, we promise it’s not gremlins”).

I suspect that the box might be a biasing array for driving the two output transistors, but then I would also expect two wires to come out of it (one for each transistor) rather than a single combined wire.

Broadcom’s datasheet for their version of the part seems to be more akin to what I’m thinking:

Image

Could be either. You’d have to decap the chip to find out, the datasheet writers thought these details were not important.