VEINS OF THE HEAD AND NECK — JUGULAR VEINS 683 



1. The last fourteen dorsal intercostal veins (Yv. intercostales dorsales) of the 

 right side go directly to the vena azygos; but on the left side a variable number 

 (four to seven usually) at the end of the series go to the vena hemiazygos when that 

 vessel is present. 



2. The vena hemiazygos arises from a branch of the left first lumbar vein and 

 twigs from the crura of the diaphragm. It passes forward through the hiatus 

 aorticus and continues along the left dorsal face of the aorta, and about the mid- 

 dle of the back joins the vena azygos. It receives the last four to seven dorsal 

 intercostal veins of the left side. It is inconstant and variable. In its absence 

 its tributaries join the vena azygos. 



3. The oesophageal vein (V. oesophagea), satellite of the oesophageal artery, 

 joins the vena azygos as it inclines downward. 



4. The bronchial vein (V. bronchialis) unites with the preceding to form a 

 short common trunk, or, according to Chauveau, empties into the great coronary 

 vein. The author is unable to find in the horse any distinct bronchial vein 

 emerging at the root of the lung.^ 



VEINS OF THE HEAD AND NECK 

 Jugular Veins 



The jugular veins (Vv. jugulares), right and left (Fig. 556), arise behind the 

 ramus of the mandible, about two and a half inches (ca. 6-7 cm.) below the tem- 

 poro-mandibular articulation by the union of the superficial temporal and internal 

 maxillary veins. Each passes downward and backward, at first embedded more 

 or less in the parotid gland, and continues in the jugular furrow to the thoracic 

 inlet, where it unites with its fellow and the two brachial veins to form the anterior 

 vena cava. In the neck it is covered by the skin, fascia, and cutaneus muscle, and is 

 superficial to the carotid artery, from which it is separated in the anterior half of 

 the region by the omo-hyoideus muscle.^ It contains valves at the mouths of its 

 tributaries, and has several pairs of semilunar valves variably disposed along its 

 course. Its tributaries are as follows: 



1. The internal maxillary vein (V. maxillaris interna) is larger than the external 

 maxillary. It may be considered to begin as the continuation backward of the 

 buccinator vein where that vessel crosses the alveolar border of the mandible, 

 about two inches (ca. 5 cm.) behind the last molar tooth. It runs backward on 

 the medial surface of the ramus ventral to the lateral pterygoid muscle, and covered 

 by the medial pterygoid muscle for a distance of about three inches (ca. 7-8 cm.), 

 then inclines a little downward and runs ventral to the artery for about an inch 

 (ca. 2-3 cm.). It crosses the lateral face of the artery at the posterior border of 

 the jaw, and is joined by the superficial temporal vein to form the jugular. Its 

 principal radicles are the following: 



(1) The dorsal lingual vein (V. dorsalis linguae) is not a satellite on any artery, 



' In Chauveau- Arloing-Lesbre the statement is made that " the bronchial veins, which ramify 

 on the bronchi like the arteries of which they are satellites, open into the great coronary vein very 

 near its mouth, after having united to form a single vessel, which sometimes opens directly into 

 the atrium. " The arrangement is not illustrated. EUenberger and Baum state that the bronchial 

 and oesophageal veins open into the vena azygos separately or by a common trunk. Martin de- 

 scribes a short broncho-oesophageal tnmk, but the vein which he figures as the bronchial does not 

 come from the lungs, but is a small mediastinal vessel. The author finds such a vessel usually 

 entering' the terminal part of the oesophageal vein, but no distinct bronchial vein in the horse. 

 The statement and figure in Bossi's recent work agree substantially with those of the German 

 authors. 



2 There is usually only one jugular vein on each side in the horse, but in some cases there is an 

 internal or deep jugular vein which accompanies the carotid artery and ends at the confluence of 

 the external jugulars. M'Fadyean records a case in which the vein lay on the deep face of the 

 omio-hyoideus with the carotid artery. This would appear to be an instance of remarkable de- 

 velopment of the internal jugular in place of the usual external jugular vein. 



