152 bulletin: museum of comparative zoology. 



for which is given on page 175. After immersion in this fluid for from 

 three to five days, the material was carried through several changes of 

 70 per cent alcohol, in which the excess of picric acid was, to a large 

 extent, removed. The head was then allowed to stand until needed in 

 a mixture of alcohol and glycerin. It was found that this^ treatment, 

 which was suggested to the writer by Mr. W. A. Willard, differentiates 

 well the nervous from the muscular tissues, and, aided by the use of 

 the dissecting microscope, makes possible the tracing out of the distri- 

 bution of veiy slender bundles of neuraxons. 



In preparation for the detailed study of the more important and 

 complicated relations of the nerves under consideration another method 

 was adopted. Certain portions of the contents of the orbit were re- 

 moved entire, care being taken to avoid straining or breaking the parts, 

 and placed for fixation in either Zenker's fluid, osmic acid or the vom 

 Eath mixture mentioned above. After dehydrating in alcohol, and im- 

 bedding in paraflSn, serial sections of suitable thickness -were made. 

 The sections were cut in planes either at right angles to, or parallel 

 with, the axis of the main trunk of the oculomotor nerve (see Plate 1, 

 Figs. 1 and 2). The sections of the material fixed in Zenker's fluid 

 were stained in acid-fuchsin. The osmic acid and vom Rath preparations 

 needed no subsequent treatment for the differentiation of the medullated 

 neuraxons. 



Cells of the ciliary, the Gasserian (cerebro-spinal) and sympathetic 

 ganglia were studied in the following manner, with a view to deter- 

 mining the number and character of their processes. The ganglia were 

 removed from a freshly killed fowl and immersed in a 0.05 per cent 

 solution of chromic acid, in which they were allowed to stand and 

 slightly macerate for two or three days. They were then carefully 

 teased apart with fine needles, and stained in acid-fuchsin. In this 

 way a certain number of cells, retaining longer or shorter portions of 

 their processes, were isolated from the rest of the ganglion, and prepared 

 for examination. Other ganglia were fixed in the vom Eath mixture 

 and studied in the form of serial sections. 



b. Anatomy. 



1. Eye-Musde Nerves and Ciliary Oanglion, 



Oculomotor Nerve and Ciliary Ganglion. The nidulus of the oculo- 

 motor nerve lies in the ventral portion of the mesencephalon, near the 

 mesocoele or aqueduct of Sylvius, in relation to which it occupies a 



