NERVES OF THE DOGFISH 305 



part, mesial and lateral of the olfactory lamellae in the antero- 

 dorsal portion of the olfactory cup, and to a smaller mesial por- 

 tion of the lamellae in the posteroventral part. The fila enter- 

 ing the lateral group of glomeruli are from the larger lateral part 

 of the lamellae of the posteroventral portion of the cup, and from 

 a smaller number of the lateral lamellae of the anterodorsal part 

 of the cup. In brief: the lateral olfactory glomeruli are related to 

 the lateral olfactory lamellae in the olfactory cup ; the mesial glo- 

 meruli are connected with mesial lamellae and with some of the 

 lateral ones. Thus there are two olfactory nerves: a ventro- 

 mesial olfactory nerve, related on the one hand to dorsal, mesial, 

 and ventral glomeruli, and on the other to mesial and lateral 

 lamellae in both parts of the olfactory cup; and a lateral olfactory 

 nerve, related to lateral glomeruli and to lateral lamellae in both 

 parts of the cup. Hence the two divisions of the olfactory cup 

 are not in exact correspondence to the two olfactory nerves, as 

 Locy supposes. The lateral division of the olfactory fila evi- 

 dently corresponds to Sund's primary olfactory nerve, and the 

 mesial division to the secondary nerve, but later distributions of 

 fibers have obscured the original sharp distinction between the 

 two nerves. In Mustelus the relations of the olfactory fila to 

 the olfactory cup and parts of the olfactory bulb are essentially 

 as in Squalus. 



In figure 1 is shown a cross-section through the anterior por- 

 tion of the olfactory bulb, where the olfactory glomeruli are seen 

 arranged in two groups: a dorsal-mesial-ventral series and a lat- 

 eral series. The two large masses of olfactory fila, ventromesial 

 and lateral, give a distinctly double appearance to the anterior 

 part of the bulb (figs. 35, 51, 52, 53, bolfm., bolfl.). Figure 2 is of 

 a cross-section through the two olfactory nerves slightly posterior 

 to the transverse level where the nervus terminalis passes across 

 the mesial olfactory fila. Some of the lateral olfactory fila are 

 seen passing mesially into the mass of mesial fila (folfm. ad I.). 

 In figure 3 the posterior edge of the anterodorsal olfactory lam- 

 ellae is shown, and in figure 4 the anterior extremities of the 

 posteroventral lamellae. The position of the septum between the 

 two parts of the olfactory cup is indicated in figures 35 and 51. 



