(Source:http://www.google.co.in/#hl=en&sa=X&ei=DAE9UPTVJs3MrQe60YDACQ&ved=0CBsQBSg
A&q=Ball+Socket&spell=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=7ee0a650f1619acf&biw=1341&bih=581 ;
24A&B:http://www.google.co.in/#hl=en&output=search&sclient=psyab&q=Ball%26Socket+
Joint&oq=Ball%26Socket+Joint&gs_l=hp.12...1570.10880.0.13115.17.17.0.0.0.0.0.0..0.0...
0.0...1c.GBIshZyTYbY&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=7ee0a650f1619acf&biw=13
41&bih=581 ; Aug. 28, 2012)

A ‘ball and socket’ is a joint in which the bone situated at a distant is capable of motion in all the directions and multiple number of axes, having one common center (plate 24 A&B). It enables the bone to move in any planes (almost all directions). In a ball and socket (spheroid) joint, the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. Among the most common familiar example that we know is shoulder-joints have the ball and socket mechanism. Shoulder joints help us to bending in multiple direction rotations. With the help of similar principle designers have created large number of ball and socket bending mechanism (plate 24C-D). Joining two rigid members with various facilitate the bending movements that are essential to most of the living beings including human beings.

NITINOL: Nitinol is a ‘shape memory alloy’ (SMA)

The behaviour of sapling’s elasticity to bend and return to its original position is quite natural and found in nature. However, an interesting metal called Nitinol developed in the Naval Ordnance Laboratory in 1962 shows amazing characteristics that can remember. The discovery of the ‘metal that remembers’ was accidental. The story is the following, “Their remarkable properties were discovered by accident. A sample that was bent out of shape many times was presented at a laboratory management meeting. One of the associate technical directors, Dr. David S. Muzzey, decided to see what would happen if the sample was subjected to heat and held his pipe lighter underneath it. To everyone's amazement the sample stretched back to its original shape.”
(Ref. http://en.wikipedia.org/wiki/Shape_memory ; Aug. 25, 2012)

The amazing discovery of the smart material that remembers its original shape Nitinol is a ‘nickel-titanium’ alloy metal that has shown some unusual properties that has memory. It is also known as ‘the metal with memory’. “It can be formed into shapes such as a helical (in the shape of a coil, helix) spring. It can then be pulled out of that shape, for example stretched outward.