SEA-FISHERIES LABORATORY. 293 



2. R. spinosus, c (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 (r. v. b + 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. The 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 



