246 COMMON CAROTIDS. 



The Carotid Arteries. 



The two carotid arteries above mentioned have been deno- 

 minated Common or Primitive Carotids, to distinguish them 

 from their first ramifications, which are called Internal and 

 External Carotids. 



The Common Carotids 



Proceed towards the headon each side of the trachea : at 

 first they diverge, but they soon become nearly parallel to each 

 other, and continue so until they have ascended as high as the 

 upper edge, of the thyroid cartilage, when they divide into the 

 Internal and External Carotids. 



These arteries are at first very near each other, and rather 

 in front of the trachea ; they gradually diverge and pass back- 

 wards and outwards on the sides of it, and of the resophagus, 

 until they have arrived at the larynx. In the lower part of 

 the neck they are covered by the sterno-mastoidei, the sterno- 

 hyoidei, and thyroidei, as well as by the platysma myoidei 

 muscles. Above, their situation is more superficial ; and they 

 are immediately under the platysma myoides. 



On the inside, they are very near the trachea and larynx, 

 and the O3sophagus ; on the outside, and rather anterior to 

 them, are the internal jugular veins ; and behind, on each side, 

 are two important nerves called the symphathetic and the par 

 vagum. These blood-vessels and nerves are surrounded by 

 absorbent vessels. 



The Common Carotid Arteries send off no branches from 

 their origin to their bifurcation ; and they appear to preserve 

 the same diameter throughout their whole extent. In some 

 few instances the right carotid has been found larger than the 

 left. The external and internal branches into which they 

 divide, are nearly equal in the adult ; but it is supposed that 

 the internal is the largest during infancy. The relative position 

 of these branches is also different at the commencement from 

 what it is afterwards. The Internal Carotid forms a curve 

 which projects outwardly, so as to be exterior to the External 

 Carotid, while this last proceeds upwards, and rather back- 

 wards. 



