Blood Arteries supplying the Head and Brain

The term Carotids come from the Greek word karotides.  The Carotids are the principal arteries which, arising from the brachiocephalic arteries, ascend the neck and supply the head and brain with blood. They exhibit several modifications which were significantly investigated by Nitzsch and by Garrod; but their taxonomic value is limited. They show the following seven arrangements :-
1. The right and the left carotids converge towards the middle line and run side by side (or the left covering the right) in a furrow along the ventral surface of the cervical vertebrae. This is their normal and original condition, and is found in the majority of birds.

2. The two carotids fuse into one, for the greater length of the neck; this "carotis conjuncta" is generally imbedded in a special median osseous canal formed by the vertebrae; the right and left root or basal portions are both functional, although one of them is sometimes weaker, as in Herodii, Phoenicopterus, and some Old-World Parrots.

Diagram of some of the variations of the Carotid Arteries

A.....Normal conditions, two separate deep carotids; 
B.....The two deep carotids fused into one, e.g. Ardea ; 
C.....The same as B, but the root of the left carotid is reduced, e.g. Phoenicopterus ; 
D.....The left deep carotid is lost, but supplanted by a superficial vessel, e.g. certain Psittaci.
su.d.....A. subclavia dextra 
su.s.....A. subclavia sinistra
c.p.d.....A. carotis profunda dextra
c.p.s.....A. carotis profunda sinistra 
c.p.c.....A. carotis profunda conjuncta
c.s.s.....A. carotis superficialis sinistra
3. There is one carotis conjuncta, but the right root, i.e. the basal portion of the original right carotis, has been obliterated. The artery is a so-called "carotis primaria sinistra." Such "Aves laevocarotidinae" (as called by Garrod) are very frequent, e.g. Rhea and Apteryx among the Ratitae, Podicipes, several Steganopodes, Alca, Otis, Turnix, Megapodiidae, some Old-World Psittaci, Merops, Buceros, Upupa, Trogonidae, Cypselidae, Colius, all the Pici and Passeres.

4. One carotis conjuncta, but the right root alone is present, the left being obliterated. "This carotis primaria dextra" is likewise deeply lodged, as in the 2nd and 3rd cases, and has hitherto been observed only in Eupodotis.

In the following three cases, one or two collateral and superficially-placed arteries take the place of one or both deep carotids.
5. A carotis primaria s. profunda dextra coexists with a carotis superficialis s. collateralis sinistra. All the American and a few Old.WorId Parrots are such "Aves bicarotidinae abnormales" (Garrod).

6. Two superficial carotids, a right and left, are present, the deep or primary vessels being entirely obliterated. This was observed by OttIey (P.Z.S. 1879, p. 461), as an individual variation of Bucorvus abyssinicus.

7. The only carotis is a carotis superficialis sinistra, all the other vessels being lost, observed by Forbes in Orthonyx spinicauda (not in O. ochrocephala), this being the only exceptional case of all the Passeres examined at his time.

It is clear that the 2nd case is directly referable to the 1st, that the 3rd and 4th are each independently developed from the 2nd, and that the 5th, 6th, and 7th cases are recent and very qualified modifications.  The undoubtedly independent acquisition of these carotid characters renders them valueless for taxonomic purposes, except within smaller and well-defined groups, e.g. the Parrots (see also VASCULAR SYSTEM).


Home to discover more interesting bird biology information at The Wonder of Birds

This page ©