BLOOD-VASCULAR SYSTEM OF THE LORICATI 85 



the auditory vein anastomoses with the ccrebclhtm vein (PI. Ill, 

 figs. 23 and 25 ; Cer.V.), which arises in and leaves the cere- 

 bellum with the cerebellum artery, but below it. In its ventral 

 course it receives a superficial branch from the posterior surface 

 of the optic lobe, and, after uniting with the auditory vein, the 

 combined trunk continues cephalad a short distance between 

 the optic lobe and the hypoaria and ventrad of the posterior 

 cerebral artery before receiving the mesencephalic vein (See 

 fig' 23). The mesencephalic vein (PI. Ill, figs. 23 to 25 ; Me. 

 V.) arises from the floor of the mesencephalon (optic lobe) and 

 penetrating ventrad through the crus, passes out between the 

 optic lobe and the hypoaria, in front of the III nerve and 

 mesencephalic artery, then crossing below the nerve and artery 

 it unites with the common vessel formed by the anastomoses of 

 the auditory and cerebellum veins to form \\\q. posterior cerebral 

 vein (figs. 23 to 25 ; P. Cer.V.). The course of this vein is 

 cephalad, directly below the posterior cerebral artery, between 

 the optic lobe and hypoaria, and between the trigemino-facial 

 complex and the IV nerve. Uniting with the anterior cerebral 

 vein midway between the cerebrum and the optic lobe it forms 

 the encephalic vein (Pis. I, II and III, figs, i, 15, 23 and 25 ; 

 Enc.V.), which shortly leaves the IV nerve to follow trigemino- 

 facial complex, and when the facialis portion of the ramus 

 lateralis accessorius is given off the cranial cavity vein is re- 

 ceived. This vein (PI. Ill, fig. 24; C.C.V.) follows along the 

 anterior surface of this nerve and anastomoses caudad with a 

 branch of the posterior encephalic vein, which follows along 

 the posterior surface of the vagus portion of the ramus lateralis 

 accessorius. Hence the venous blood from the adipose tissue 

 of the cranial cavity may reach the jugular vein through the 

 encephalic, or the posterior encephalic vein, or through both. 

 Then leaving the trigemino-facial complex, along the inner 

 surface of the ciliary nerve, the encephalic vein penetrates with 

 it through the most anterior foramen in the prootic, and here 

 empties into the internal jugular just before it unites with the 

 orbitonasal and external jugular in forming the main jugular 

 vein. 



{c) Orhito-nasal Veins (Pis. I, II and III; figs, i, 5, 13, 15, 



