| OCR Text |
Show 458 MR. A. H. GARROD ON THE [May 6, of the thorax it divides into the carotid, vertebral, and thyroid branches, except in those in which the carotid of one side is deficient. In what may be called the typical arrangement, the carotids, equal in size or nearly so, run up the front of the neck from the inner side Fig.l*. Fig. 2. Fig. 1. Carotids at the base of the neck in aves bicarotidince normales. Fig. 2. Carotids at the base of the neck in aves Icevo-carotidince. of each thyroid gland, converging until they meet in the middle line, at which spot they enter the median intermuscular septum, and continue up to the head, on the front of the bodies of the remaining cervical vertebrae, in the hypapophysial canal, covered by the lateral cervical muscular masses, and, where they are present, threading the bony arches. Birds with this arrangement are said to have two carotids, and may be termed aves bicarotidince normales (see fig. 1). A second group is peculiar in having the right carotid branch of the inuominate undeveloped, when the left only traverses the hypapophysial canal, being of large size; it bifurcates shortly before it reaches the head, thus producing a vessel on each side, to be distributed in the same way as the terminations of the carotids in the previous group. Such birds are said to have a left carotid, and may be termed aves Icevo-carotidince (see fig. 2). In a third arrangement, found only in certain Parrots (see fig. 3), the right carotid artery runs in the hypapophysial canal, and the left at the side of the neck superficially along with the corresponding * In these diagrams, which represent the main arteries at the root of the neck, the following is the explanation of the abbreviations:-h, origin of the aorta at the heart; a, arch of the aorta; l.i, left innominate artery ; r.i, right innominate artery; l.s, left subclavian, and r.s, right subclavian artery; I.c, left carotid, and r.i; right carotid artery. |
