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DR J. STUART THOMSON ON THE MORPHOLOGY OF THE 
The tractus olfacto-corticalis medio-clorsalis has been described by Johnston in 
Acanthias as continuing in a caudal direction until it meets the pallial tract as 
the latter proceeds anteriorly over the tractus olfactorius lateralis. He states 
that when the pallial tract and the olfacto-corticalis medio-dorsal tract meet and 
intermingle the number of fibres in each has diminished very much, and that both 
enter the lateral border of the primordial hippocampus. The distribution of this 
tract appears to vary in Elasmobranchs. It has been found to be large and promi- 
nent in Acanthias, but has not been recognised in Scyllium. In Spinax its distribu- 
tion appears to differ from that in Acanthias, as apparently it does not extend in 
a caudal direction to meet the pallial tract. It appears that this tract runs from 
the paraterminal body to the primordial hippocampus, and then passes on to the 
formatio pallialis. 
Tractus cortico-medialis, Botazzi, Ga.upp, and Kappers ; tractus olfacto- 
corticalis septi, Johnston, etc. ; fasciculus medianus, Catois. — Some ventral 
fibres of this tract are seen in fig. 7. They pass dorsally on either side from the 
ental surface and medial end of the tuberculum olfactorium. Though not shown 
in my figure, I have traced long continuous fibres passing far dorsally (internal to 
the medial walls of the lateral ventricles) and external to another set of fibres 
(see figure) lying nearer the medial line, which will be described under the title 
tractus medianus in a later paragraph.* With the exception of one difference, 
this tract apparently agrees with the course described by Johnston. The main 
facts are that in the so-called “ septum ” the fibres form a very diffuse bundle 
dorso-ventral in direction, that the bundle collects from the ental surface of the 
medial part of the tuberculum olfactorium and passes up into the primordium 
hippocampi. In fig. 34, p. 82 of his paper on the “Telencephalon of Selachians,” 
Johnston gives a drawing combined from several transverse sections* to show the 
relations of the so-called “ fornix ” and the tractus olfacto-corticalis septi in Scyllium 
caniculi. In his drawing the tractus olfacto-corticalis septi is represented as 
extending dorsally as far as the upper extremity- of the lateral ventricles. This 
is at least not true for Spinax, in which the fibres of this tract only extend into 
the paraterminal body or the ventral part of the primordium hippocampi. My 
other drawings of the distribution of this tract agree with those of Johnston which 
are not combined, and I am therefore inclined to suspect that an error may possibly 
be present in his combined drawing. Johnston terms this tract the tractus olfacto- 
corticalis septi, but I retain the older name, the tractus cortico-medialis of Botazzi 
and Kappers, etc. 
Tractus olfacto-corticalis medialis cruciatus. — Regarding this tract Johnston 
writes (p. 16) : “In the area of secondary fusion of the medial olfactory nuclei in 
Acanthias appear a few medullated fibres (figs. 58, 59, 69), which arise in the 
* Fig. 8 shows the fibres of the tractus cortico-medialis situated lateral to the fibres of the more medial 
tractus medianus. 
