CELL MASSES IN THE FOREBRAIN 399 
bundles and its dendrites wrap around and penetrate the bundle. 
The formation of glomeruli in the course of large bundles of fila 
is a condition similar to that in Petromyzon described by the 
writer (1902). In addition to these large glomeruli are numer- 
ous smaller ones formed by the dendrites of small brush cells 
and of granule cells. 
The formatio olfactoria consists then of (1) an enormous num- 
ber of granule cells whose bodies form the dense peri-ventricular 
layers and whose rather straight dendrites radiate outward to 
form glomeruli or to mingle with dendrites of other cells in 
glomeruli; (2) a peripheral layer of mitral cells and small brush 
cells presenting a great variety of forms, whose dendrites form 
the large glomeruli by ramifying in the bundles of fila olfactoria; 
and (3) of the incoming fila olfactoria and the afferent and 
efferent fibers connecting the bulb with the rest of the brain. 
The gross structure known as the olfactory bulb in the turtle 
consists of formatio olfactoria and nothing else. While the 
hippocampal formation and the pyriform lobe both push forward 
into close contact with the olfactory formation, the groove which 
marks the peduncle corresponds accurately to the line of division 
in the internal structure. The so-called ‘nucleus olfactorius 
anterior in this brain is very clearly distinct from the granule 
cell layer of the olfactory bulb and does not extend forward 
beyond the peduncular constriction. 
TRACTUS OLFACTORIUS 
At the olfactory peduncle the fibers of the olfactory tract 
(figs. 55, 56, 57) have the following disposition. The largest 
bundles lie on the lateral surface and pass caudad into the 
pyriform lobe. These fibers arise from the greater part of the 
lateral and from the dorsal surface of the bulb. On the dorsal 
surface of the peduncle a large bundle, which has its origin in 
the dorsal part of the medial wall, crosses obliquely from the 
medial to the lateral surface and joins the bundle last mentioned. 
These constitute the lateral olfactory tract. Its further course 
will be described in connection with the pyriform lobe. Fibers 
arising from the remaining ventral and medial parts of the bulb col- 
