ULOOD-VASCULAR SYSTEIM OF THE LORICATI 9I 



3. hifcrior Jugidar Veins. 



These vessels return the venous blood from the ventral mus- 

 culature of the head, heart, and ventral portion of the branchial 

 arches and correspond in the main to the pharynx artery. The 

 inferior jugular vein, however, does not become a paired vessel 

 until near its termination in the precaval vein. 



The inferior jugular vein may be said to arise from a small 

 vein coming from the ventral surface of the tongue, the lingual 

 vein (PL II, fig. 12 ; Lin. V.). This vein continuing caudad 

 as the inferior jugular vein, passes in a median line above and 

 between the h3^ohyoideus superior muscles, after which it re- 

 ceives 3 pairs of veins, the first pair coming from the outer 

 posterior surface of the geniohyoideus muscles, the second from 

 the inner surface of the hyohyoideus superior muscles (PI. II, 

 fig. 12; Hys.V.), and the third pair are the ventral nuti'ient 

 branchial veins from the first branchial arch. The latter ves- 

 sels (PI. II, fig. 12 ; N.Br.V.) drain the ventral half of the first 

 pair of arches. Each of them arises as a paired vessel in front 

 of the first efferent branchial artery. The nutrient filament 

 veins (PI. I, fig. 2 ; N.Fil.V.) from one side empty into one of 

 these branches and those from the opposite side into the other 

 branch.^ Further caudad these two branches unite forming a 

 single nutrient branchial vein into which a few of the most 

 ventral nutrient filament veins from both sides are poured. In 

 front of this nutrient branchial vein, running along the cephalic 

 margin of the arch, is another vein, which sends caudad cross- 

 vessels that empty into the main ventral nutrient branchial vein. 

 Continuing ventrad, cephalad of the efferent branchial trunk, 

 the first ventral nutrient branchial vein empties into the inferior 

 jugular vein. After collecting these veins the inferior jugular 

 passes caudad, above the thyroid gland and the ventral aorta ; 

 receiving branches from the gland, other ventral nutrient branch- 

 ial veins, and several small veins coming from the obliqui ven- 

 trales muscles. Emerging from the last pair of afferent bran- 

 chial arteries the inferior jugular continues caudad, passing 



' It is of interest to note that the nutrient filament veins comefrom the inner 

 margins of their filaments ; while the nutrient filament' arteries are distributed 

 to the outer margins. 



