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Show 464 MR. W. OTTLEY ON THE GROUND-HORNBILL. [June 3, from the comes nervi vagi, 2, and which also furnishes several branches to the syrinx and its muscles. And, lastly, the innominate divides into subclavian and vertebral. From the former, S, only one branch, the acromial thoracic, at, is seen to spring, before the artery escapes from the thorax. The latter, V, soon sends a branch downwards, D, which runs with the recurrent laryngeal nerve, and ends by supplying the bronchus, the lung-substance, and the oesophagus. The next branch, 2, is the comes nervi vagi, which runs up the neck with the vagus nerve, and ends by anastomosing with the vertebral. In its course it supplies :-(a) a branch to the thyroid gland, Gl; (b) a series of vessels forwards to th& oesophagus, where they form loops and supply several branches to the trachea as well as "to the skin; (c) near the head a small offset to the internal pterygoid muscle. After this the vertebral gives off a suprascapular artery, Ss, and a superior intercostal (which from its lying behind tbe vertebral cannot be represented) to the upper three spaces ; and between these two and the branch 2 a wbite thin cord springs from the inside of the vertebral, and, crossing, inwards beneath the comes nervi vagi, gets beneath the oesophagus to the hypapophysial canal. Here it is joined by its companion of the opposite side ; and these cords run up the neck side by side till near the fourth cervical vertebra, when they bend outwards, get from beneath the pharynx, and end by joining the vertebral truuk (as seen in the second plan of vessels), just after this artery has sent off that branch which furnishes the internal carotid. It thus appears that the two true carotids are obliterated, while their duty is performed by a superficial vessel on each side, which, accompanying the vagus as it does, might be called the comes nervi vagi, though by its position in the neck this vessel rather resembles the true carotid of Mammalia. These vessels did not differ much in size ; the right was somewhat larger; but the vertebrals were almost precisely symmetrical. As a result of this change in the vascular supply of the neck, the arrangement of the vessels in the upper part of the neck and in the bead was a good deal modified. In the place of an anastomosis between the vertebral and an occipital branch of the carotid, the vertebral, which is large, turns forward and completes an arch with the superficial comes nervi vagi, whose concavity is joined by the obliterated carotid, while its convexity furnishes the branches for the head. The following is a short description of their course and distribution (vide fig. 2, p. 465). After the vertebral artery has turned forwards out of the canal in the cervical transverse processes, its first branch (18) is distributed to the m uscles attached to the back of the head. Another small branch (11) is given downwards to reach the digastric and internal pterygoid. A large vessel (10) then comes off, which soon enters a bony canal behind the tympanum (the limits of which are marked by tbe transverse lines in the plan), and divides into two (20, 21); the upper vessel (20) turns behind the fenestra ovalis (F 0),and, then emerging from its canal, furnishes a large offset to the orbital plexus |