316 THE INTERNAL JUGULAR. 



When it has arrived at the atlas, the Vertebral vein sends 

 branches to the contiguous muscles of the neck. It also fre- 

 quently sends a branch through the posterior condyloid fora- 

 men of the occipital bone to the lateral sinus. 



It is evident, from these circumstances, that the vertebral 

 vein carries a portion of blood from the sinuses of the brain 

 and of the spinal marrow, as well as from the muscles of the 

 neck, into the subclavian veins. 



The veins of the head are frequently very different in differ- 

 ent subjects. 



The Internal Jugular, 



Already mentioned, is almost exclusively appropriated to 

 the cavity of the cranium ; and all the exterior veins of the 

 head are ramifications of one or more smaller vessels, which 

 pass up superficially on the neck, and are denominated Exter- 

 nal Jugulars. In some instances almost all the exterior veins 

 of the head are united to the internal jugular at the upper part 

 of the neck, and it of course conveys the blood of the exterior 

 as well as of the interior parts of the head. Frequently these 

 veins are divided between the internal and external jugulars, 

 but they are divided very differently in different subjects. 



The Internal Jugular, however, almost always passes in the 

 same direction from the inside of the origin of the sterno-mas- 

 toid muscle to the posterior foramen lacerum of the cranium. 

 It is deeply seated on the external side of the common carotid 

 artery, and under the sterno-mastoid muscle. Between the 

 upper margin of the thyroid cartilage and the angle of the 

 lower jaw, it often sends off branches which are very different 

 in different subjects, but commonly pass to the anterior parts 

 of the neck and face: above these it generally sends another 

 to communicate with the external jugular. One of the branches 

 which often go off from the internal jugular is that which cor- 

 responds with the superior thyroid or laryngeal artery. This 

 vein, which has sometimes been called the Guttural, sends 

 many ramifications to the thyroid gland. The Ranular veins, 

 which are so conspicuous under the tongue, are also deriyed 



