The brain of Acipenser. 255 
tr. sac-thal tractus sacco-thalamicus, consisting of fibres from the epi- 
thelial cells of the saccus 
tr.strio-thal tractus strio-thalamicus; asc ascending portion; desc de- 
scending portion; ven ventral bundle, composed of both ascending 
and descending fibres 
tr.thal-mam tractus thalamo-mammillaris 
tr.thal-sac tractus thalamo-saccus; consisting of fibres from the region 
of the corpus geniculatum to end freely in the saccus epi- 
thelium. 
tr. tect-bulb.c and r tractus tecto-bulbaris cruciatus et rectus 
tr. tect-cereb. I and II the two portions of the tractus tecto-cerebellaris 
tr. tect-lob.c and r tractus tecto-lobaris cruciatus and rectus 
tr. tect. str.? tractus tecto-striaticus (or tractus strio-tectalis); “Mantel- 
'  biindel” 
v ventral roots of cranial nerves 
v.med.a velum medullare anterius. 
Plate A 
Phot. 1. Brain of fish 11/, meters long, in cartilage. Left side 
exposed by cutting away cartilage and removing the greater part of 
the packing tissue. The left half of the choroid plexus of the IV 
ventricle is removed. The VI nerve was pulled away in preparation, 
owing to the extreme delicacy of its rootlets, Photographed out of 
water, in consequence of which numerous points of high light appear. 
Bl. 
Phot. 2. Brain of another fish 1!/, meters long, median hemi- 
section. Cartilage undisturbed immediately dorso-cephalad from the 
tip of the pineal gland. Under water. X 1. 
Phot. 3. Same preparation X 3, to show detail of interior surface. 
Pater. 
Phot. 4. Lateral aspect of same brain as in Phot. 1, all choroid 
plexuses removed. Under water. X 2. 
Phot. 5. Same brain, dorsal aspect, with choroid plexus of IV 
ventricle and roof of dorsal sack removed. The lobus inferior and 
saccus vasculosus appear on the left side, but were covered by carti- 
lage on the right. The same is true of the V, VII and VIII nerves, 
Roof of fore brain torn. Under water. X 2. 
Phot. 6. Same brain with choroid plexus of fore and ’tween brains 
removed. Under water. X 2. 
Phot. 7. Same brain, with cerebellum and tectum removed by 
cutting through crura and side walls of mid brain. Internal surface 
of mid brain and cerebellum. Under water. X 2. 
