SEA-FISHERIES LABORATORY. 291 



wards on the inner surface of the abdominal wall, and just 

 under the peritoneum. This ramus supplies the ventral 

 musculature and ventral skin. In the region of the 

 appendages the limb girdles and fins are supplied from 

 R.R. ventrales. In the specimen now investigated, how- 

 ever, the fourth spinal was not connected with either the 

 pectoral or pelvic appendage. The fourth R. ventralis 

 anastomoses below with the nerve r. v. 2 + 3 1 , as described 

 below. 



The First Spinal Nerve. 



This nerve is a compound of at least two spinal nerves, 

 since it has two ganglia and most of its principal rami 

 are in duplicate. It is, however, here described as the 

 first spinal, on account of the difficulty of completely 

 isolating its constituents. 



The ganglia and roots of the first spinal are situated 

 in the bony tube formed by the exoccipital, and leading 

 from the foramen magnum into the cranial cavity proper 

 (see fig. 4). There is one main foramen for the nerve, 

 which tunnels transversely the narrowed base of the par- 

 occipital condyle, as shown in fig. 3 (above the lower letters 

 Ex. 0.). Another smaller foramen for the R. spinosus b. 

 is situated immediately above this, and occasionally there 

 is another larger one immediately below it for the R. 

 ventralis, as shown in the chart. Usually, however, the 

 latter nerve passes through the main foramen. There are 

 thus at least two foramina for the first spinal nerve, and 

 there may be three — all situated in the exoccipital. 



The first spinal has two perfectly distinct ganglia — 

 an intracranial ganglion (g. inter.), and an extracranial 

 ganglion (g. e.vtcr.). These two ganglia are connected by 

 a large bundle of sensory and motor fibres which pass 

 through the main foramen (indicated in the chart by the 



