THE VASCULAR SYSTEM 245 



branes of the Brain', p. 123, et seq.). These do not arise periodically 

 along the whole length of the vessel, but almost exclusively from 

 near its origin, and at its anterior end. They are drained by the dorso- 

 median vein of the cerebrum. 



(b) The dorsal branch, R. cerebralis anterior dorsalis (Osawa) 

 (Arteria lobi haemisphaerici superior interna, Scholb) passes dorso- 

 mesially round the thalamencephalon to the paraphysial region 

 (nodus chorioideus. Rex), giving on its way a branch to the posterior 

 and mesial regions of the cerebral hemisphere. 



(i) The mesial cerebral artery passes anteriorly along the mesial face 

 of the hemisphere somewhat obliquely in a dorso-ventral direction. 

 This vessel does not appear to have been previously described unless 

 it corresponds with the 'posterior dorso-median vein of the fore- 

 brain' of Rex, which otherwise has not been found. 



At the nodus chorioideus the dorsal cerebral artery sends a few 

 small branches to the plexus and then turns ventralwards and divides 

 into two branches. 



(ii) One branch supplies the lateral plexus of the first ventricle 

 (pl.ch.ven.i). The artery enters the ventricle through the foramen 

 of Monro, and within it forms a very beautiful coiled plexus. If this 

 plexus is carefully flattened out it is found to be roughly triangular 

 in shape, with the artery bordering the perpendicular and base, and 

 the veins gathering towards the apex. 



(iii) The other branch supplies the inferior median plexus (Burck- 

 hardt's plexus chorioideus inferior), a small, but rich plexus lying in 

 the recessus praeopticus. 



The superior median plexus appears to be supplied usually by a 

 branch from the right dorsal cerebral artery. This branch comes 

 off just as the main vessel turns ventralwards. The plexus is long, 

 tapered to a point at its posterior end, and flattened laterally. It lines 

 in the dorsal part of the cavity of the diencephalon. 



It should be noted that the right and left dorsal cerebral arteries 

 are not always equal in size. Either may develop at the expense of 

 the other. 



(II) Ramus posterius (Scholb) or R. cerebralis posterior (Osawa). 

 This branch passes directly mesialwards to a point on the ventro- 

 lateral border of the midbrain, just at the posterior border of the 

 infundibulum and anterior to the origin of the Ilird nerve. Here it 

 breaks up into four branches. 



{a) R. opticus ^Vf\i\Q\s. ramifies fan-wise over the side of the optic lobe. 



(^) The R. pituitarius which passes round the infundibulum to its 

 ventral surface and then turns posteriorlytosupply the pituitary body. 



