Why is this strange law still on the books, or is it?

In Massachusetts, it's supposedly against the law to drive with a gorilla in the back seat of your car, according to Nationwide. I tried to find the specifics in the Massachusetts General Laws, but came up short. However, in my Google search, I came across an article that clarified a few laws which would make having a gorilla in your car illegal, even though the word "gorilla" is not used. For example, Mass. Law Libraries states:

No person shall transport an animal in the back of a motor vehicle in a space intended for a load on the vehicle on a public way unless such space is enclosed or has side and tail racks to a height of at least 46 inches extending vertically from the floor, the animal is cross tethered to the vehicle, the animal is protected by a secured container or cage or the animal is otherwise protected in a manner which will prevent the animal from being thrown or from falling or jumping from the vehicle.

There is also a Massachusetts law about the "importation, transportation, and possession of endangered species," which would include gorillas.

The third law which would make it illegal to have a gorilla in your car is actually a federal law. Mass. Law Libraries mentions federal law 9 CFR 3.87 regarding permits and the "transportation of nonhuman primates."

So, the long answer to our question is: Yes, it is illegal to have a gorilla in the back seat, or any part of your car.