Third Cord 
1Tc MEER (i ees Tas, 
| tie anterior | posterior 
bes I era lumen| fibre | lumen| fibre 
B 13 H HM f 
Larval Lepidosteus (1,5 cm) 1,2 20 1,2 15 {0g 
| ‚6 
» 4Amia calva (1,7 cm) | — 20 1 2 0, 4 
| 10 0,9 
Ps ; =: keer CHL) -- 15 1 4 0,6 
| \3 | 06 
» . Ameiurus (2 cm) | 0,8 — |— 6 0,5 
Acanthocottus aenus (12 cm) 9 — | — — _ 
Morone americana 3 =~ 3 -- 2,5 
Cynoscion regale | 6 40 6 20 6 
Pomatomus saltatrix — 45 | 10 — —_ 
Lophiatilus chamelionticeps 9 90 8 _ — 
Roccus lineatus — _ A ze _ 
Stenotomus chrysops _ — 25 | — _ 
Microgadus tomco 3 _ 3 _ _ 
Salvelinus fontinalis — _ 3 — _ 
Palinurichthys perciformis — — 2,5 _ _ 
Lophius piscatorius —_ 50 5 _ — 
Tylosurus marinus 50 2,5 a _ 
Tautoga onitis = 25 4 _ _ 
Opsanus tau _ 50 15 45 1,5 
Pseudopleuronectes americana — 30 3 — _ 
Necturus maculata — 30 2,5 - — 
Anolis sp. — 15 2,5 | 12 2,5 
Scelopterus undulatus (8 cm) _ 16 1,4 12 12 
E » (14 em) = 75 | 18 10 = 
Alligator mississippiensis (20 cm) 3 30 3 25 3 
Eutainia sirtalis (20 cm) sat 15 | 15 10 nF 
Columba livia (pigeon) _ 25 18 | — = 
Mus musculus 1 60 | _ | 1 
In cross sections of the spinal cord REıssner’s fibre may usually 
be found lying near the center of the lumen of the canalis centralis. 
In such sections, it is inconspicuous, as it is small, usually 2 w or less 
in diameter, and is often further obscured by the presence around it 
of corpuscles and loose cells. In thin sections the fibre is likely to 
drop out or become displaced, since it is so slightly supported in the 
relatively large lumen of the canal, which is usually from ten to twenty 
times the diameter of the fibre. In cross sections the fibre is best 
studied in those forms where it is large, as in Cynoscion, Pomatomus, 
and Lophiatilus, in which it attains a diameter of 10 «. In such 
sections the fibre shows a circular outline, and its cylindrical form is 
clearly made out by focussing. In series of transverse sections the fibre 
can be followed from section to section throughout its course. Cross 
