THE NERVOUS SYSTEM OF THE BIRD 195 
Fig. 47 Hen. Transverse section at a level slightly below the preceding section. Marchi stain. 
p.l.b. Degenerated posterior longitudinal bundle. 
Fig. 48 Hen. Transverse section through the upper part of the pons, showing descending degenerations 
in the columnar fibres resulting from a lesion higher up. Marchi stain. 
ant. Anterior columnar fibres. antJat. Anterior lateral columnar fibres, lat.col. Lateral 
columnar fibres. 
Fig. 49 Hen. Transverse section through pons, showing descending degenerations from lesion at a low 
level of the mesencephalon on the same side. Marchi stain. 
Letters as above. 
Fig. 50 Hen. Transverse section of cervical region of spinal cord, showing the anterior and lateral 
degenerations from a lesion at a low level of the mesencephalon of the same side. 
Marchi fluid stain. 
Plate X. Figs. 51 — 55 
Fig. 5 1 Brain of Pigeon seen from dorsal aspect. 
c.p. Position of excitable area which produces contraction of pupil of opposite eye. Pec. 
Position of excitable area which produces complex movements of rotation of head, 
pecking, and deglutition. Olf. Olfactory lobe. Cer. Cerebral hemisphere, r. Dorsal 
ridge. Op.v. Optic lobe. med. Medulla. 
Fig. 52 Brain of Pigeon seen from ventral aspect. 
A. Tr. septo-mesencephalicus. F. Tr. occipito-frontalis. A.C. & E. Anterior com- 
missure and Tr. occipito-mesencephalicus. 
Fig. 53 Brain of Pigeon seen from the lateral aspect, showing position of excitable areas, cp. tff Pec. 
Fig. 54 Cells of the pallium. Nissl stain. Showing cell clusters, in obj. 
Fig. 55 Transverse section through the mesencephalon, showing the position of the large cells described 
originally by Stieda in the lamina commissuralis mesencephali. 
a. These cells highly magnified, y.^ in. obj. 
