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it issues from its foramen, and while still in this tissue, and lying 

 posterior to the opticus, separates into its two terminal branches. The 

 cerebral branch continues upward and forward, and piercing the mem- 

 branous side wall of the skull posterior to the opticus enters the 

 cranial cavity, its further course not being traced. The branch of the 

 carotid destined to the eye ball also runs upward and forward posterior 

 to the opticus, but it does not enter the cranial cavity. It lies at 

 first in the postero-lateral wall of the mass of dense connective tissue 

 that surrounds the issuing opticus, and there separates into its two 

 terminal branches. These two branches continue upward and forward, 

 cross a portion of the space enclosed within the dense connective tissue, 

 and then enter the dorsal, or dorso-lateral wall of the mass of tissue. 

 There they soon issue from the tissue, and separating reach the eye 

 ball, one piercing it on its dorso-anterior surface and the other ventro- 

 posterior and close to the opticus perforation. The further course of 

 the two arteries was not traced, my sections not permitting it, but the 

 one that accompanies the nervus opticus is evidently the art. retinalis, 

 the other one being doubtless an iris artery. The retinalis is quite 

 unquestionably the artery called by McKenzie the ophthalmica magna, 

 but as there is no choroid gland in Ameiurus this identification of the 

 artery is manifestly an error. 



No arteries other than the two above described were found 

 entering the eye ball at any place, and Mc Kenzie dsscribes but the 

 one of these two, his ophthalmica magna. McKenzie, however, finds 

 three encephalic arteries, instead of but one, as I find, all of his 

 three arteries arising from the so-called pseudobranch, and all said 

 to be distributed wholly to the brain. The anterior one of the three 

 is said to be connected with its fellow of the opposite side, beneath 

 the optic chiasma, by a transverse commissure, the posterior one also 

 being connected with its fellow of the opposite side, but by fusion with 

 it, in the median line, immediately behind the saccus vasculosus. 



The orbito-nasal artery runs forward along the floor of the orbit, 

 passing ventral to the nervus opticus and ventral also to the points 

 of origin of the recti externus, internus, superior and inferior, the latter 

 two of which muscles have their origin definitely from the mass of 

 tissue that surrounds the issuing opticus, while the former two arise, 

 partly at least, from the so-called orbitosphenoid, immediately ventral 

 to the tissue. From the tissue there also arises a strong fibrous 

 strand, evidently an eye stalk, which runs outward and has its inser- 

 tion on the eye ball dorso-posterior and close to the opticus per- 

 foration. At the anterior end of the orbit, the orbito-nasal artery. 



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