The Design Changes on the Endoskeleton

TERMINATOR 3 : RISE OF THE MACHINES

So where did the post Cameron sequels take the design? In Terminator 3: Rise of the Machines, the digital endoskeleton from the opening had teeth that were actually going inside the skull, as if into gums, rather than being on the skull as it is with real human skulls. However, that questionable alteration was made by CG team only, the Winston skull retained the original look.

TERMINATOR SALVATION

Amazingly, the baby teeth had also made it into the reshaped CGI form in Terminator Salvation as well, while the prop skulls had the correct full size teeth

Salvation reshaped the endoskeleton , mainly its proportions. The CG endo is considerably beefed up and proportioned like a bodybuilder. The first reason is that they added a lot of new parts to the Terminator Salvation endoskeleton that didn't exist on previous endoskeletons. Some of the parts add bulk, while others fill in what would have been empty spaces in the endoskeleton chassis. With all that extra clutter, the endoskeleton looks more solid and less skeletal. On the Terminator Salvation endoskeleton, the inner sides of the upper arms have an additional support that doesn't exist on previous endoskeletons. The outer sides of the upper arms have curved structures that bulk out the arms. In the torso area, there are a lot more tubes than there used to be. At the shoulders, there are multiple tubes that run to them, and they connect to a part on the shoulder that doesn't exist on older endoskeletons. The second reason is that they changed the design of certain parts. The pelvis was narrowed compared to previous endoskeletons. The spinal column was also changed. In previous endoskeletons, the spinal column was tapered so that it was widest at the base. But in Terminator Salvation, the spinal column is tapered so that it was narrowest at the base. Those changes also help minimize any empty space within the confines of the chassis. 

Together, those changes minimize empty space while simultaneously increasing bulk and visual complexity

There are also several changes made to the skullface. The teeth alter the design considerably, but there are several changes in the shape and design. The cheekbones have different shape, rounded as opposed to squar-y, there are no indentations on them, the nose is much narrower and so is the shape of the skull and designs on it, and the proportions and eye sockets differ as well. It also has lips, which explains the small teeth

TERMINATOR GENISYS

Terminator Genisys ignored and discarded not only the previous two stories, but their redesigns as well. For Terminator Genisys, the endoskeleton got an interesting body redesign which updated it to modern sci-fi style, to a more sleeker scifi look. Notably the chestplate resembles the Cyberdyne logo now, the arms are closer to the shape of human's, so is the spine and the pelvis area. The proportions reverted back to the original design.

The skull has minor alterations - the jaw is thinner and the actual skull is now, for the first time, symmetrical. The skullface also reverted back to the original design

Also, for the first time, the CG and puppet endos match perfectly