The 78xx series voltage regulator IC

[bitrex]

I'm trying to understand the operation of the 78xx series voltage regulator IC from the schematic in the data sheet, and am having a lot of trouble. Analysis of some of the older voltage regulator ICs seems straightforward but to a newb this circuit looks like alien technology - I'm having trouble even identifying any functional units. Does anyone have any tips?

http://i227.photobucket.com/albums/dd240/bitrex2007/7815.jpg