1538 
from the second spinal sympathetic ganglion (com. 77.), 
and sends a mixed bundle to the R. ventralis of the first 
spinal nerve as above described (r. v. 21). Just at about 
the same place it fuses completely with the R. ventralis of 
the third spinal nerve, but the above anastomosis is 
derived from the R. ventralis 2, and contains no fibres 
from 3. The compound trunk (7. v. 2+3), after giving off 
‘a small branch to the inner surface of the clavicle (not 
shown in the chart), courses forwards and downwards, and 
gives off below two motor branches which pass at first 
downwards and then forwards to supply the ventral 
musculature. They anastomose with each other close to 
their origin, and the posterior one (r. v. 2+ 51) also anasto- 
moses below with the R. ventralis of the fourth spinal 
nerve. The temainder of the trunk then splits behind 
into two—a small motor nerve and a larger mostly sensory 
nerve. The latter (r. v. 2+”) is continued backwards on 
to the ventral portion of the pectoral fin. 
Phe Third Spanal Nerve. 
This spinal nerve has the usual two roots (d. 3 and 
v 3), and a single very large extra-vertebral ganglion 
(g. 3). Each root has a separate foramen in the neural 
arch of the second vertebra (fig. 17). The sensory R. 
€ 
communicans (r. com. 3) contains a few motor fibres, which 
are liberated as a small bundle for the dorsal musculature 
(not shown in the chart). It fuses with the R. spinosus 2, 
as above described. The motor R. spinosus (r. sp. 3), 
after rising internal to the ganglion, courses at first back- 
wards, fuses with the R. communicans 4, and then turns 
forwards as a mixed nerve high over the roof of the skull 
and very close to the middle line. It gives off below the 
motor nerve to the dorsal musculature just like the pre- 
ceding nerve. 
