Houser, Zhe Neurones of a Selachian. 149 
HUCHTEN ('94) has noted their presence in the trout, and 
JOHNSTON (’98a) in the sturgeon. 
The cell-nucleus has its chromatin disposed in slender, 
branching threads, and in minute granules distributed somewhat 
diffusely (Fig. 66). The cytoplasm forms a thick investment 
to the nucleus on all sides. Its tigroid masses are markedly 
larger than those found in the neurones of the epistriatum. The 
largest ones lie in the bases of the dendrites, and these have a 
triangular form. Other masses of smaller size and of more 
irregular shape are intercalated between the larger ones. Ti- 
groids extend into the dendrites for a short distance, only. 
The axone takes its origin directly from the cell-body, so 
far as observed (Fig. 35). It gives off collaterals during the 
first part of its length. The several axones descend to the base 
of the forebrain and run posteriorly in the tractus strio-thala- 
micus for ultimate termination in the thalamus; see Section 
VII. This conspicuous fibre-tract was described by Ronon 
(77) as the pedunculus cerebri ; by SANDERS (86) as the crus 
cerebrt ; and by EpINGER in his earlier work (’88) as the dasale 
Vorderhirnbiindel. 
The general striatum has the type of structure and the 
associations which are characteristic of motor centres. The 
large neurones, with their long and widely spreading dendrites, 
enter into a nexus with the axones derived from a purely sen- 
sory centre, the epistriatum. The latter receives, chiefly, im- 
pressions of the olfactory order. The neurones of the striatum 
are indirectly affected through the axones of the epistriatum, 
carrying, in turn, the nervous disturbance to the interbrain, 
whence a relay carries it to the great roof-nucleus of the mid- 
brain for direct connection with the neurones of the body mus- 
culature. The enormous olfactory organs of Mustelus indicate 
how important the olfactory sense must be in the economy of 
the animal, and observation demonstrates the large place taken 
by olfactory impressions in the location of food. The striatum 
is evidently the centre for motor reflexes, of which the sensory 
neurones chaining the olfactory organ to it constitute one arm, 
