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2. R. spinosus, ¢ (r. sp. c.).—Large motor nerve from 
the third ventral root. It perforates the intracranial 
ganglion dorsally, passes a little backwards in order to 
leave the skull by the foramen magnum above, and then 
courses forwards and upwards. Arrived at the roof of the 
skull, it bends forwards over the latter, at first lying over 
the epiotic a little to the side of the narrowed posterior 
portion of the supraoccipital. It then fuses in the typical 
manner with the sensory R. communicans of the second 
spinal nerve, to form a conspicuous mixed nerve which 
courses forwards over the roof of the skull near the middle 
line to its distribution. 
3. R. ventralis (7. v. 6+c)—This usually leaves the 
skull by the main foramen, but it occasionally has a 
foramen of its own situated below the main foramen, and 
above the paroccipital condyle, as in the specimen figured. 
It has a comparatively slight connection with the extra- 
cranial ganglion, but the latter ganglion does undoubtedly 
contribute fibres to it. The R. ventralis is formed as 
follows :—First of all the remainder and greater part of 
the first and second ventral roots, having passed under- 
neath the intracranial ganglion, and together with some 
sensory fibres, pass into the special foramen (indicated by 
a ring in the chart). They are immediately followed by 
the remainder of the third ventral root (also accompanied 
by sensory fibres from the intracranial ganglion), which, 
having perforated the intracranial ganglion, and instead 
of passing into the main foramen as usual, turned down- 
wards and entered the special foramen. ‘he ventral root 
thus left the skull by all three foramina. These two mixed 
trunks more or less unite in the foramen, and immedi- 
ately outside it in this specimen bore a small number of 
discrete ganglion cells. The latter, however, undoubtedly 
belong to the extracranial ganglion. The two trunks soon 
