Using jq is there an easy way to combine json objects into an array

I have two simple jsons that I want to combine into one. I am trying to bake this into some automation so that I will not need to manually combine the two each time. Is there a way with jq to combine file1.json with file2.json so that the output looks like desired.json?

file1.json

[
  [
    "1",
    "2"
  ],
  [
    "a",
    "b"
  ]
]

file2.json

[
  [
    "3"
  ],
  [
    "c"
  ]
]

desired.json

[
  [
    "1",
    "2",
    "3"
  ],
  [
    "a",
    "b",
    "c"
  ]
]