90 ALLEN 



of the second and third dorsal nutrient branchial veins. The 

 combined vessel thus formed passes dorsad behind the second 

 levator arc. branch, internus muscle, and after receiving a 

 branch from it and another from the second obliquus dorsalis 

 muscle, terminates in the jugular. In this specimen the third 

 and last dorsal branchial muscle vein arose from 2 branches. 

 The most cephalic one is a dorsal nutrient branchial vein from 

 the last branchial arch, and the other has its source from the 

 pharyngo-clavicularis externus, pharynx, and the occipito- 

 clavicularis muscle. The dorsal branchial vessel thus formed 

 passes in a dorso-cephalic direction above the corresponding 

 artery. After crossing the last efferent branchial artery it 

 receives a good-sized branch coming from the last 2 internal 

 branchial levator muscles, and then empties into the jugular 

 directly behind the second dorsal branchial vein, but before 

 emptying into the jugular it receives the thymus vein from the 

 rear. This vein (fig. i ; not lettered) runs cephalad along the 

 ventral margin of the gland, receives several branches from it, 

 and shortly before reaching the anterior end of the thymus, 

 curves ventrad ; crossing over the posterior encephalic and 

 jugular veins, finally terminates in the third dorsal branchial 

 muscle vein shortly before the latter empties into the jugular. 

 In another specimen from the one figured, the dorsal nutrient 

 vein from the second branchial arch joined the first dorsal bran- 

 chial muscle vein immediately after it had pierced the first 

 levator arc. branch, internus muscle. The second dorsal 

 branchial muscle vein took its origin from the third dorsal 

 nutrient branchial vein and received branches from the third 

 obliquus dorsalis muscle and the second levator arc. branch, 

 internus muscle ; while the third and last dorsal branchial 

 muscle vein had its source from the fourth nutrient branchial 

 vein and a branch coming from the fourth obliquus dorsalis 

 muscle. The thymus vein emptied into the posterior encephalic 

 vein, and the vein from the phar3mgo-clavicularis externus, 

 pharynx, and the occipito-clavicularis muscle, which is usually 

 the source of the last dorsal branchial muscle vein, crossed the 

 jugular and posterior encephalic veins and terminated in the 

 thymus vein. 



