84 OSBORN. (Vou. II. 
closely with those of Cryptobranchus. We first observe that 
the lobes of the infundibulum (Fig. 14) are united dorsally and 
ventrally by commissural fibres as in the Uvodela (Osborn, ’84, 
Plate IV., Fig. 4, scm, icm). The two sides of the tectum opti- 
cum are also united by an almost continuous band of transverse 
fibres, Fig. 11, fem, as in the Amphibia, terminating anteriorly 
in a special enlargement, fce, Fig. 17, which I identify as the 
posterior commissure. The bande fibrillaire laterale of Fig. 15, 
fl, is probably either the posterior commissure or Mey- 
nert’s bundle. The bundle connecting the ganglia habe- 
narum, in Fig. 18, fgf, is probably the superior commissure. 
The upper bundle 7%, Fig. 19, and ff, Fig. 20, in the lamina 
terminalis, is probably the corpus callosum; this is an im- 
portant fact, if verified, since this commissure has not heretofore 
been definitely identified below the Amphibia! This can only 
be verified by following the course of its fibres. The lower 
bundle, Fig. 19, ca, occupies a somewhat unusual position, upon 
the floor of the brain. 
Two differences in the internal structure may be noted : first, 
the optic chiasma is intra-axial or central, instead of periph- 
eral, as in the Amphibia; second, there is a single pair of 
large Mauthner fibres in the medulla oblongata, which are 
wanting in most of the Uvodela,? although the posterior lon- 
gitudinal fasciculus is apparently present, 77, sp, Fig. 1. 
I cannot institute any satisfactory comparison in respect to 
the origin of the cranial nerves. Many minor points of re- 
semblance and difference have been passed by in this resumé, 
the general conclusion being that there is a very close 
similarity between the Amphibian (Urodele) and 
Dipnoan brain, both in the external and internal 
structure. 
COMPARISON WITH PETROMYZON. 
One of the chief features of Ahlborn’s memoir upon the 
brain of Petromyzon is the thoroughness with which he has in- 
1JIn concluding my paper upon the corpus callosum (Morph. Jahr., Band 
XII., p. 539), I had not seen Fulliquet’s memoir, but anticipated from the embry- 
ology of the Ceratodus fore-brain, that this commissure would be found in the Dipnoi 
2 They have been observed by Stieda in Siredon, see Appendix, Note 5. 
