Courtesy of Gray's Anatomy
The left spermatic cord is rather longer than the right, consequently the left testis hangs somewhat lower than its fellow. The spermatic cord's external aspect varies under different circumstances: thus, under the influence of warmth, and in old and debilitated persons, it becomes elongated and flaccid; but, under the influence of cold, and in the young and robust, it is short, corrugated, and closely applied to the testes.
Diagram
If you look at the diagram you can see that where the spermatic cord exits the penis it spits into two cords. One which turns to go straight down to the testis the other to go on a more convoluted path, consequently longer.
(This was not an exact quote since there were medical terms scattered practically every other word in the text. If you want to read it directly from the source here's a link where you can find it.
Grey's Anatomy )