hi there, it does look like a nasty cut and first of all you will need to clean up the wound with warm water and antiseptic lotion and remove all the dead and necrotic tissues from the wound. next you should give him a light antiseptic dressing where you do not tie the wound but just protect it from dirt and insects, with a gauze bandage and plaster. Keep the limb elevated and give him some anti inflammatory and pain killers. He needs to also receive a shot of tetanus toxoid
injection. Observe for a day if the inflammation starts subsiding and he has symptomatic relief then you may contineu dressing up the wound everyday and inti-inflammatory pills but if not then you do need to visit an ER and get it examined by a doctor and if required started on antibiotics Take care.