A 22 y/o male patient presents to your emergency department…

A 22 y/o male patient presents to your emergency department via ambulance in a semiconscious state with medics holding pressure to a wound on his forearm. Upon inspection, you note a deep laceration to the lateral proximal forearm ejecting bright red blood at a regular, fast interval concurrent with the patient’s heart rate. Based on your observation, which blood vessel has MOST LIKELY been lacerated?