Difference between extends and uses stereo types in Use Cases

The "<<uses>>" stereo type specifies the use case "A" will use the use case "B" atleast once. For e.g. say there are 2 use cases "Send Message", "Encrypt Message". Everytime the use case "Send Message" is used, in turn the "Send Message" will use the "Encrypt Message" use case.

The "<<extends>>" stereo type specifies the use case "A" is special general type of use case "B". For e.g. say there are 3 use cases. "Send Message", "Send Mail Message", "Send Fax Message". Here the the "Send Message" is a general type of "Send Mail Message" and "Send Fax Message"