THE NERVOUS SYSTEM OF THE BIRD 179 
MuNZER and Wiener's work is a complete and important contribution to the study of the 
tracts of the central nervous system, and the degenerations they undergo. In most essential points 
the independent conclusions arrived at by these writers and ourselves are in agreement. 
In this place it is unnecessary to mention the older observations, to which a complete 
reference is given by Friedlander, or the researches on the fine cellular anatomy of Ramon y 
Cajal, van Gehuchten, and Kolliker.* 
NAKED EYE LANDMARKS OF THE BIRD'S BRAIN 
The paramount importance of the visual apparatus in the bird is indicated by the size of 
the optic nerves and chiasma ; the transverse section of an optic nerve being as large as that of the 
dorsal region of the spinal cord. On the other hand, the olfactory lobes are very small. 
The cerebral hemispheres are well developed, and for purposes of description may be 
roughly divided into anterior, middle, and posterior lobes (Plate IV, fig. 7). As we shall see, these 
lobes give origin respectively to different groups of nerve fibres. 
Fissures on the surface of the brain are not well marked. We draw attention, however, 
to one which runs from before back on the dorsal surface about yVth inch on each side of the 
median plane, and forms the external boundary of an area which is excitable by the faradic 
current, the stimulation resulting in well-marked pupillary contractions (Plate X, fig. 51). 
The main tracts of nerve fibres are fairly obvious as prominent white strands of tissue. 
On carefully separating the hemisphere there is seen — 
(1) On the mesial aspect, the fan-shaped tractus septo-mesencephalicus, disappearing just 
in front of the transversely running anterior commissure (fig. 40, Plate IX). 
(2) Beneath this commissure, the united fibres of the tractus striothalamicus and 
striomesencephalicus (fig. 40, Plate IX). 
When the brain is placed with the ventral surface uppermost there appear : — 
(1) The superficial termination of the tractus septo-mesencephalicus, a well-formed strand 
of fibres situated along the junction of the cerebral hemispheres with the optic lobes and thalamus 
(fig. 52, Plate X). 
(2) Laterally, on the hemisphere, the great associational system between the posterior and 
anterior parts of the brain (fig. 52, Plate X). 
(3) The prominent white fibres covering the surface of the optic lobes. 
On transverse section of the hemispheres the origin of the striothalamic tract and anterior 
commissure is well seen (fig. 52, Plate X). 
DESCRIPTION OF TRACTS 
The various tracts of the central nervous system fall into the following groups ; — 
1. Tracts in connection with the great cell mass of the hemisphere. 
2. Optic chiasma and tracts in connection with it. 
* Since this paper was read Edinger and Wallenberg have published in the ' Anatomischer Anzeiger,' Band 15, 1899, a 
communication, entitled ' Untersuchungen iiber das Gehirn der Taiiben.' In this the various tracts and cell nuclei are described 
in detail, and the previous work of the authors incorporated. 
