THE SUPERIOR CAVAL SYSTEM. 863 



The left internal jugular has been observed much reduced in size, there being a compen- 

 satory enlargement of the corresponding external jugular, and it may be doubled throughout a 

 greater or less portion of its course, although always single at either extremity. In addition 

 to the normal tributaries described below, it may receive the temporo-maxillary vein, the verte- 

 bral, superior laryngeal, or left superior intercostal, a bronchial vein, the suprascapular, or the 

 transverse cervical vein. 



Practical Considerations. — The internal jugular vein — the largest of the 

 superficially placed veins of the body — may be involved in cut-throat or other wounds 

 of the neck. Like the carotid, it usually escapes in attempts at suicide on account of the 

 usual position assumed — with the chin elevated and the head thrown back so that the 

 muscles are rendered tense and prominent and the vessels are protected. If the 

 wound is above the thyroid cartilage they are still safer on account of their inclination 

 backward, and such a wound may reach the spinal column without injuring them. In 

 wounds below the thyroid if the air passages are opened in attempted suicide, the 

 sudden exit of air from the lungs, accompanied by collapse of the chest, may, it has 

 been suggested, result in the dropping of the arm carrying the weapon before the 

 wound has reached the level of the vessels, although they are here more vulnerable 

 than they are above. The internal jugular, the other veins of the neck, and the 

 subclavian and axillary veins, are greatly influenced by respiration, emptying during 

 inspiration, distending during expiration — the "respiratory wave," or "venous 

 pulse." Their attachments to the fascia keep them from entirely collapsing. This 

 is especially noticeable in the internal jugular. After the carotid sheath has been 

 opened the vein will vary in appearance from a distended thin-walled tube perhaps 

 half an inch in diameter, (expiration), to a flaccid, ribbon-like structure with walls 

 apparently in contact (inspiration). During inspiration air may thus be readily drawn 

 into one of these veins if it has been wounded, and if the wotuid is dry, or if pressure 

 is not immediately applied to the vein on the cardiac side of the wound. If the air is 

 in large quantity it may cause instant death when it reaches the right atiricle by over- 

 distension and paralysis of the right side of the heart ; or sometimes less rapidly by 

 asphyxia following air embolism of the pulmonary veins. 



The internal jugular vein may be infected secondarily to infective intracranial 

 sinus thrombosis, especially of the sigmoid. Phlebitis or thrombosis of the internal 

 jugular is attended by pain and tenderness along the course of the vein, and later by 

 the development of a cord-like mass to the inner side of the sterno-mastoid muscle 

 and the outer side of the carotid artery. This may involve the whole length of the 

 vein but is apt to be confined to the upper third. When an infected thrombus in the 

 sigmoid sinus has undergone such extensive disintegration that it is unlikely to be 

 entirely removed by operative obliteration of the upper two-thirds of the sinus, or 

 when in a thrombosed internal jugular, giving the sensation of a hard cord-like struc- 

 ture, its upper part becomes soft from disintegration of the thrombus and this disin- 

 tegration descends, ligation of the vessel below this point usually becomes necessary 

 (Macewen). The ligation shuts of? the main channel between the sigmoid sinus and 

 the lungs, although the latter may still be infected by way of the occipital sinus and 

 condylar veins and the subclavian vein. 



The vessel is approached by the same incision as that made for ligation of a caro- 

 tid. The vascular sheath is opened well to the outer side so that the carotid com- 

 partment may, if possible, be left intact. The vein should be tied in two places and 

 divided between the ligatures. 



After occlusion of the vein either by ligature or by pressure from a growth, the 

 blood from the corresponding side of the head passes by a transverse vein to the 

 internal jugular of the opposite side. 



Tributaries. — In addition to the lateral and the inferior petrosal sinuses, which 

 will be described with the other cranial sinuses, the internal jugular receives the 

 following tributaries : (i) the pharvns:eal, (2) the facial, (3) the Imgiial, (4) the 

 stiperior thyroid, and (5) the inidd/e t/ivroid \e\ns. 



I. The Pharyngeal Veins. — The pharyngeal veins (w. pharyngeae) are small 

 vessels, varying in number, which open, either independently or after having united 

 to a single stem, either directly into the internal jugular or indirectly by way of the 



