662 
sheath opposite the origin of the transverse processes only. Elsewhere 
a narrow space intervenes. The ensheathing bone of each segment has 
the form of two truncated cones placed with their apices together. 
The majority of the spinal nerves leave the canal by special fora- 
mina in the neural arch, the intervertebral foramina being closed 
by membrane (Fig. 2). 
The relation to the cartilaginous arch in the young explains the 
phenomenon and robs it of any significance for the thesis of double 
vertebree. In a young 
specimen of Speler- 
pes fuscus of 39mm 
length, the following 
arrangement was found. 
The first three spinal 
nerves pierced the bony 
arch in front of the car- 
tilaginous Anlage. The 
fourth left the spinal 
canal by the inverte- 
bral foramen. The fifth 
pierced the arch of the 
fourth vertebra behind 
the cartilage. The seg- 
Fig. 2. Spelerpes fuscus, juv. Horizontal section of last trunk and sacral 
vertebre. Bone shaded, cartilage dotted. N. neural arch. g. spinal ganglia. 7. trans- 
verse process. Ji. ileum. For. interv. intervertebral foramen. 
ment in which the change occurs is not constant, as in an adult 
specimen it was the third nerve which left the spinal canal by the 
intervertebral foramen, and the fourth obtains exit by a special foramen 
in the neural arch of the third vertebra. In the succeeding trunk and 
tail vertebr& the like arrangement holds, except for a few of the ter- 
minal caudal segments where the nerve again leaves by the inter- 
vertebral foramen. Hence the nerve of each body segment posterior 
to the third or fourth as the case may be, leaves the spinal canal 
by a foramen in the arch of the vertebra of the preceding segment. 
In reality, in spite of the extension of the spinal cord to the tip of 
the tail, it is shorter than its bony canal; or, in other words, the 
bony canal has outgrown the spinal cord. 
The transverse processes are rib-carriers, “Rippenträger” G@&PPERT!). 
1) E. Gapprrt, Morphologie der Amphibien-Rippen. Festschrift für 
CARL GEGENBAUR, 1896. 
