Some medications, (as alison suggests nitroglycerine is one of these) are absorbed quite quickly when placed under the tongue. This is the sublingual route.

Bald Eagle, you're right,the tongue is a muscle. In intralingual administration the tongue is lifted and the medication injected directly into its underside. You're pretty well assured the patient is out cold when he tolerates this. Intralingual administration is no longer indicated in our practice on the street. The reason we used to do this is that the uptake of the medication is rapid through this route and in a patient with scarred veins it provides easy access. Nowadays we manage the airway and wait for the intramuscular injection we've stuck in the arm to take effect.