162 JULIA WORTHINGTON. 
The motor cells of the medulla are gathered in two main 
groups, a lateral and a ventral motor column. ‘The latter is 
the continuation in the medulla of the ventral horn of the 
spinal cord. It is comparatively small, and lies near the 
median line, ventral to the commissural fibres of the median 
raphé, and continues cephalad nearly to the anterior end of 
the medulla. It gives fibres to the vagus, but so far I have 
not been able to find any fibres going from it to the other 
nerves. Near its anterior end, about the level of the hind 
end of the cerebellum, it contains a number of cells of 
Mauthner, very large and irregular in shape. The lateral 
motor column begins at the lind end of the medulla and 
runs along its ventro-lateral angle as far forward as the 
motor trigeminus. It consists of three divisions, an 
anterior, closely packed sphere of cells, a middle division, in 
which the cells lie farther from each other and without 
definite arrangement, and a posterior division, where the 
cells are arranged in several longitudinal rows. This last 
division supplies the vagus and glosso-pharyngeus. 
The facialis draws its motor fibres mainly from the posterior 
half of the middle division, though taking a few from the 
anterior half. Most of the cells of the anterior half of the 
middle division, and all of those of the anterior division, 
send their fibres into the trigeminus. 
The two sides of the medulla are connected along its entire 
length by a system of commissural fibres, which seem to 
come from all the regions of the medulla, and which cross in 
the median raphé immediately ventral to the fourth ventricle. 
Toe CRANIAL NERVES. 
Bdellostoma has only seven of the ten to twelve cranial 
nerves found in most vertebrates, viz. the olfactorius, 
opticus, trigeminus, facialis, acusticus, glosso- 
pharyngeus, and vagus. Of these the olfactory and the 
trigeminus are the largest and most strongly developed, 
