ON THE ANATOMY OF FISHES. 
99 
Nusbaum, Grassi, and himself, that the intercalariurn is identical with the neural 
arch of the second vertebra. 
The foramen for the first spinal, or " hypoglossal ” nerve, traverses the exoccipital, 
and is seen internally just over the roof of the cavum sinus imparis (fig 5, sp.n.'), but 
externally is visible immediately in front of the external atrial aperture (figs. 1, 4, and 
9, sp.n.'). The dorsal and ventral roots of the second and third spinal nerves traverse 
distinct paired foramina in the fibrous wall of the neural canal between the neural 
plate of the exoccipital in front and the arch of the third vertebra behind. The roots 
of the second nerve pass outwards between the ascending processes of the scaphium 
and intercalariurn, the foramen for the dorsal root being situated near and a little 
behind the upper extremity of the scaphium, and the one for the ventral root at a 
much lower level (figs. 4 and 5). The foramina for the roots of the third nerve lie 
comparatively close together between the ascending process of the intercalariurn and 
the arch of the third vertebra (figs. 4 and 5). The roots of the fourth spinal nerve pass 
outwards from the neural canal through a single foramen in the anterior part of the 
arch of the third vertebra {sp.n.‘^) ; those of the fifth nerve through a pair of foramina 
near the posterior margin of the arch of the fourth vertebra [sp.n.^) ; and similarly 
the roots of the sixth nerve through a pair of apertures in the posterior part of the 
arch of the next vertebra : and so on with the succeeding: anterior spinal nerves 
(fig. 2). 
As the roots of the first to the fourth spinal nerves, inclusive, emerge from the 
neural canal to pass to their peripheral distribution, they traverse the cavity of the 
saccus paravertebralis on the dorsal side of certain of the Weberian ossicles. The 
hypoglossal nerve crosses the interossicular ligament, and emerges from the saccus 
between the inferior limb of the post-temporal and tlie opisthotic plate of the ex- 
occipital, and immediately behind the vagus. The second and third nerves cross the 
anterior process of the tripus, and leave the saccus betw^een the inferior limb of the 
post-temporal and the anterior division of the transverse process of the fourth 
vertebra. The fourth nerve emerges from the posterior extremity of the saccus, and, 
after passing dorsad to the crescentic process of the tripus, is continued by its ramus 
ventralis along the ventral surface of the transverse process of the fourth vertebra. 
The rami ventrales of the two succeeding spinal nerves traverse the dorsal surfaces 
of the transverse processes of the fourth and fifth vertebrae respectively. As the 
rami ventrales of the fourth to the sixth spinal nerves, inclusive, pass to their peri- 
pheral distribution, tliey curve round the dorsal and lateral surfaces of the anterior 
chamber of the air-bladder, and, in the latter part of their course, lie on each side 
between the lateral cutaneous area and the lateral wall of the bladder. 
The ventral divisions of the first to the fourth spinal nerves, inclusive, are distri- 
buted to the muscles of the pectoral arch and fin, and those of the fifth and sixth to 
the lateral musculature of the trunk. 
Sagemehl (33) has described an additional spinal nerve as emerging from the 
o 2 
