In this close-up of the right half of the motherboard, we see a huge IC chip (the CPU), a prominent connector (the cartridge port), and several blue patch wires running here and there. Wires like this often signify last-minute design fixes that were soldered in by hand at the factory. It’s never reassuring, in my opinion, to see them in a shipping product—but hey, it works.
On the right side of the board is the peripheral expansion bus connector, of which you can only see its copper shielding here. TI created many peripherals for the 99/4A which plugged into the right side of the computer, making for a cumbersome expansion process. Later, they released a unified expansion box to simplify things, but it was still awkward.