Ok...you only have one cv joint.
Lets assume you have a 30 degree angle at the rear of the tcase.
A single u joint at the tcase has to absorb all the angle (all 30 deg) that is there. A cv joint uses 2 u joints in a special housing to divide the angle between them (each sees 15 deg), so no single u joint see the complete angle that is required to get from the tcase to the rear end. What this looks like from either side is no matter...there are 2 u joints in a cradle that keeps them in alignments with each other, but allows them to also move independently of each other. The is a centering ball inside that cradle that keeps the u joints from moving off center fromeach other.
If you look at yer front driveshaft, up by the tcase, you will see the same thing on it..but it is only one cv joint...actually called a cardian joint.
This is really hard to explain, but that is how it works. the whole mess at the tcase rear output is the single cv joint......it is about 6-8 " long, and has the u joints and cradle in it. If you had the same thing at the rear end, you'd have 2.
Do you understand what I mean