946 
MR. A. SANDERS ON THE ANATOMY OF THE 
tecta, so that when a transverse section is made there is nothing to prevent their 
falling apart. 
Spinal Cord. 
A section of the spinal cord shows the same features as in M. cephalus. The grey 
matter here forms a figure like a St. Andrew’s cross (figs. 13 and 14). The dorsal 
horns are not very much developed, while the ventral horns have about the usual 
appearance. These latter show the ventral ganglion with, from six to ten cells in one 
section, together with the central ganglion with seldom more than two, but these of a 
larger size. 
Three pairs of columns may be distinguished—the dorsal columns, situated between 
the two dorsal horns of grey matter; tbe lateral columns placed between the dorsal 
and ventral horns : these are characterised by tbe nerve fibres having a tendency 
to fall into separate bundles, thus differing from the corresponding columns in M. 
cephalus, where they form a more undivided mass; and finally the ventral columns, 
situated in the space between the two ventral horns ; these have the same sort of large 
fibres as in ordinary Teleostei, and contain also the characteristic Mauthner’s fibres. 
Kanvier* considers that there is no physiological significance in the various sizes of 
the nerve fibres, but still it is a curious circumstance that the ventral columns should 
always contain fibres of so much larger calibre than the others. 
The dorsal columns are traceable forward through the tuberosities, of the vagus and 
the outer and inferior angle of the tuberculum impar into the posterior and outer part 
of the cerebellum; they, together with the tuberosity of the vagus, probably homolo- 
gise with the resfiform columns or bodies and contain finer fibres than either the lateral 
or ventral column. 
The lateral columns are also composed of fine fibres, finer than those of tbe ventral 
columns, except at the part where they border on the dorsal horns. Here some of the 
fibres are of a larger size. When they arrive at the medulla oblongata, these lateral 
columns are arranged as just mentioned in separate bundles slightly resembling the 
formatio reticularis of that part in the Elasmobranchii. They can be traced forward as 
far as the large transverse commissure of the tuberculum impar, which some of them 
appear to join, others go forward as far as the inner side of the torus semicircularis, 
being joined by some fibres from the central portion of the above-mentioned commissure, 
but many of them are dispersed in the grey matter of the medulla. 
The ventral longitudinal columns are divided into two bundles by the ventral 
transverse commissure, as in M. cephalus. In the medulla oblongata further forward, 
they are separated by the immensely developed transverse decussating commissure 
(fig. 7) of the tuberculum impar. The Mauthner’s fibres accompany the upper or central 
longitudinal column and decussate immediately under the angle formed by the pos¬ 
terior root of the trifacial as it turns outward towards its place of exit from the medulla 
* Lemons sur 1’Histologie du Systeme Neryeux. Paris, vol. i, p. 100. 
