146 JouRNAL OF COMPARATIVE NEUROLOGY. 
such interest as to deserve especial notice. It appears super- 
ficially as a well-marked depression in the median plane a little 
anterior to the pallial eminence (Fig. 1, ~f.). It is rendered 
even more noticeable during life by the penetration of blood- 
vessels here, owing to which fact Ronon (’77) called it the 
foramen nutritivem. This structure is the vestige of a neuropore. 
Its ontogeny was first described from the ganoid brain by von 
KUPFFER (90) as the lobus olfactorius tmpar. RABL-RUCKHARD 
described its development in the selachian embryo (’93) ; and 
BurcKHARDT (’94d) has identified it in-many other vertebrates. 
The recessus neuroporicus of Mustelus retains the character 
of an open passage in the adult animal (Fig. 31, 7p.), serving 
as a channel for blood- and lymph-vessels. It is accompanied 
by a pair of fibre-tracts, right and left, which take this primitive. 
path from dorsum to base of the brain; see Fig. 31, m. 5s. 7. 
I. The Olfactory Lobe. 
It is my purpose to devote a future paper to the entire 
olfactory apparatus of Mustelus, and soa detailed description 
of the olfactory lobe will not be given here. For the under- 
standing of what follows, it will be sufficient to state that, in 
the bulbus, the olfactory neurones of the first order are chained 
to those of the second order through the usual tangles known 
as the olfactory glomeruli; and that the neurones of the second 
order, mitral cells, send their axones through the tractus to 
terminal stations described further on. Other neurones of the 
olfactory lobe, having a purely accessory value, need not detain 
us at present. 
2. The Stratum. 
The striatum is primarily a part of the olfactory apparatus, 
and its morphology must be interpreted with this fact in mind. 
Two groups of neurones have become defined from the general 
mass of the striatum for the especial reception of olfactory 
impressions. One of these lies next to the lateral ventricle, 
the epistriatum ; while the other one is peripheral in its loca- 
tion, the nucleus postolfactorius. The structure of the principal 
