BLOOD-VASCULAR SYSTEM OF THE LORICATI 57 



along the ventral surface of the left optic nerve, and shortly 

 before the olfactory lobes are reached they bear off laterad 

 around the optic nerves, but, before leaving them, each vessel 

 gives off a branch, which continues along the ventral surface 

 of the nerve to the eye. This is the of tic or retina artery (PL 

 III, figs. 22, 23, and 25 ; Opt. A.), which gives off branches to 

 the nerve and finally penetrates the eye-ball a little cephalad of 

 the nerve. Once inside the retina it continues along the retina 

 fissure (see fig. 22), giving off branches to either side and 

 especially to a whitish gland-like body situated on the side of 

 the fissure close to the falciform process. The main portion of 

 the artery, however, breaks up on the falciform process, the 

 campanula Halleri, and even extends over on the lens. It is 

 also probable that the retina receives nourishment from the 

 choroid arteries, which are separated from the retina only by 

 the thin pigment layer of the choroid. The main anterior cere- 

 bral artery after curving around the optic nerve divides into an 

 anterior and a posterior portion. Close to the point of bifurca- 

 tion the anterior branch sends forward a small vessel, which 

 runs along the ventral surface of the olfactory nerve, but the 

 main trunk passes inward and anastomoses with its fellow in 

 the median line. This point of union marks the source of 2 

 vessels, a smaller dorsal one designated as the most anterior 

 cranial cavity artery (PI. Ill, fig. 23 ; C.C.A.), coming up 

 between the olfactory lobes to supply the adipose tissue in the 

 anterior region of the cranial cavity and a larger caudal vessel, 

 which runs in a median line between the optic nerves and the 

 cerebral hemispheres, giving off several branches to the latter 

 through the median fissure. The posterior branch of the 

 anterior cerebral artery is a superficial vessel ; it follows caudad 

 along the ventro-lateral surface of the cerebrum, passing between 

 it and the optic nerves, and giving off superficial branches to 

 the ventral surface of the cerebrum and the anterior surface of 

 the mesencephal. Sometimes the right, but more often the left 

 artery continues dorsad with the epiphysis as the second cranial 

 cavity artery (PI. Ill, fig. 23 ; C.'C.'A/). 



i:\i^ posterior cerebral arteries (PI. Ill, figs. 23 and 25 ; P.- 

 Cer.A.) come off from the encephalic artery at right angles to 



