38^_ 



the drawing); a small one, passing obliquely backward and downward 

 to unite with the lateral division of the olfactory nerve, another, slender 

 branch , passing to the median division of the olfactory , and a chief 

 central stem (the only one represented in the drawing) which crosses 

 the median division of the olfactory nerve and dips into the fissure 

 separating the two divisions of the fila. The median division of the 

 olfactory nerve is broader than the lateral so that the point at which 

 the nerve disappears in the fissure is about two-thirds the space across. 



By widening the fissure, it can be seen that the main stem breaks 

 into a number of small branches which dip downward, until they reach 

 about the level of the median horizontal plane of the olfactory cup, 

 and then pass laterally among the fila olfactoria close to the mem- 

 branous covering of the cup. In an antero-lateral position, they pene- 

 trate the connective tissue covering of the cup and, still in close 

 association with fila olfactoria, enter the folds between the nasal epi- 

 thelium. All this, with the exception of the last point (for which 

 sections are required), can be made out by careful work under the 

 dissecting microscope, and has been many times confirmed by repeated 

 observations. One point that forcibly strikes the observer is, that the 

 fibers of the new nerve preserve their individuality after mingling with 

 the fila olfactoria. The two sets of fibers commingle very intimately, 

 but actual anastomosis between them has not been observed. 



Ganglion. — This nerve bears a spindle-shaped ganglion (gn) situated 

 in the adult near the bulbus. It should also be remarked, that the 

 ganglion is often divided into a proximal and a distal portion, and 

 that there is individual variation as to size and position of these parts. 

 The more prominent one is usually near the bulbus, and the less 

 distinct one near the brain. In addition to these, there are sometimes 

 minute clusters of ganglion-cells between the two enlargements. In 

 general structure one of these ganglia resembles a spinal ganglion. 

 It is surrounded by a covering of connective tissue, from which septa 

 and trabecular pass into the interior of the gangliou, and give support 

 to the other elements consisting of ganglion cells, nerve fibers, blood 

 vessels and lymph spaces. The gangliou cells are arranged in layers 

 and clusters between the nerve fibres and connective tissue elements. 

 The nerve-cells in this ganglion vary in size in the different genera. 

 In Squalus, although larger than the connective tissue cells, they are 

 relatively small as compared with the corresponding cells of Scyllium, 

 Trygon, and Alopias. 



Fig. 2 (A) represents a section of the ganglion in Squalus showing 

 bipolar cells (gn. cl.) and a large multipolar cell {gn. cV). The ganglion 

 cells in Alopias, as shown in Fig. 2 (B) are much larger and lie within 



