*Whitehead<unk>  invented in 1877 by Walter Whitehead (1840-1913), a surgeon in Manchester, England, consists of two hinged metal frames that wrap around the front of the patient's head and which have sections bent to fit between the front teeth. When spread apart, the frames separate the jaws, holding the mouth open. The desired degree of separation is set and maintained by a ratchet mechanism on each side of the frame. *Jennings<unk>  they are very similar, but there is a ratchet on only one side.
Gag 
Gene
Ze339
OTL-103
TRNA 
GP 
CFP-10
HBeAg