108 BULLETIN OF THE BUREAU OF FISHERIES. 



B. The spermatic or ovarian veins (13), which return blood from the genital 

 organs, run craniad in the abdominal cavity, emptying posteriorly into the Cuvierian 

 ducts. 



C. The jugular veins (15), two large vessels, one on each side, return blood 

 from the head region. Behind the orbit each jugular vein is situated directly dorsal 

 to the branchial arches and between the base of the cranium and the hyomandibular 

 bone. 



Branches of 'the jugular vein. — (a) The most cranial tributaries of the jugular 

 vein are vessels (£6) that return blood from the upper jaw and contiguous structures. 



(b) About 1 cm. in front of the orbit the jugular receives a vein {.'■'>) from the 

 olfactory organ and adjacent tissue. 



(c) Ventral to the middle part of the orbit it receives the facial vein (..'.'), which 

 is formed by the union of a vessel (24-) from the angle of the mouth and the m. 

 adductor mandibulse, and a branch (S3) which returns blood from the operculum. 



(d) Directly behind the orbit the right and left jugular veins are connected by 

 the transversely situated interorbital vein (19). This vessel (19), which is about 2.5 

 cm. in length, arches between the two jugulars and in the median line receives the 

 cerebral vein (21), which returns blood from the brain. It also receives the ophthal- 

 mic veins (SO), which, one on each side, leave the eye at a point near the entrance of 

 the optic nerve, and after passing between the rectus superior and externus usually 

 receive branches from the eye muscles and open into the interorbital not far from the 

 jugular. Sometimes, however, the vessels from the eye muscles open directly into 

 the interorbital vein. 



The jugular vein from this point continues caudad, partly surrounded by the 

 cranial end of the kidney (lv'). from which it receives branches, and opens into the 

 dorsal end of the Cuvierian duct with the posterior cardinal vein of the same side. 

 Three important vessels enter the cranial end of the kidney to empty into the jugular 

 vein: The postorbital vein (IS), which returns blood from the muscles of the head 

 behind the orbit; the pharyngeal vein (17), which returns blood from the superior 

 pharyngeal teeth, the muscles, and contiguous structures dorsal to the branchial 

 arches; and a vein (16), which returns blood from the thymus gland, muscles, and 

 membranes on the outer surface of the clavicle. These three veins (76', 17, and 18) 

 enter the cranial end of the kidney, and, after giving off several venae advehentes, 

 usually unite to form a single vessel, which opens into the dorsal surface of the 

 jugular vein. 



D. The posterior cardinal veins (1/+) lie immediately ventral to the vertebral 

 column, embedded in the substance of the kidney, and are asymmetrically developed. 

 The left (11/s) is small and its cranial portion, which is about 3 cm. long, functions as 

 a vena revehentis renalis. The right cardinal vein (1-^A) is a vessel of considerable 

 size; it receives at its caudal end a large vein (37) from the posterior division of the 

 kidney, a connecting trunk (36d) from the caudal vein, and revehent branches from 

 the kidney, as well as branches directly from the parietal veins; it then empties with 

 the corresponding jugular vein into the right Cuvierian duct. 



