192 THE LARYNX, BRONCHI AND OESOPHAGUS Under the age of 40, the thyroid cartilage is still largely cartilaginous and so, when it hits the vertebrae, the laminae are spread outwards and a fracture occurs down the prominence. When the compressing force is removed, the cartilage recoils forwards, reassurning its normal shape, but with a linear fracture down the prominence. The effect of this fracture is to detach the Fig. 94. Seat-belt injuries. A, If only a lap-belt is worn the driver is flung forwards with injury to the larynx. B, If full harness is worn this type of injury is prevented. Fig. 95. Seat-belt injury. To illustrate the two phases in the younger patient. The larynx is forced backwards on to vertebral column and the thyroid cartilage fractures down the prominence. When the larynx springs forward to regain its normal shape, the vocal cords are detached at their anterior ends. epiglottis which will now hang free in the laryngeal lumen causing obstruction. It will also detach the anterior ends of the vocal cords which may either hang into the trachea or roll up on themselves towards the arytenoid (Fig. 95). As the arytenoids are pushed against the cervical vertebrae they become bruised and swollen and perhaps even disarticulated from the cricoid.