It's used to treat strains and sprains by resting movement of the head. It's used for more neck injuries requiring longer-term treatment. It's a laminated polyurethane foam support covered with afresh collared. Stockinet and a removable slave. Collateral Circulation.-After ligature of the common carotid, the collateral circulation can be perfectly established, by the free communication which exists between the carotid arteries of opposite sides, both without and within the cranium, and by enlargement of the branches of the sub calving artery on the side corresponding to that on which the vessel has been tied. The chief communications outside the skull take place between the superior and inferior thyroid arteries, and the profound cervices and ramous descendents of the occipital; the vertebral takes the place of the internal carotid within the cranium.