7i2 ALLIS. [VoL. XII. 
cap of each arch sits directly upon the posterior face of the 
dorsal process of the next preceding vertebra, and is so inti- 
mately connected with that face that, as already stated, it can- 
not be separated from it, without fracture, even in specimens 
that have been treated with acids. The posterior face of the 
cap rests upon the anterior face of the dorsal process of the 
next following vertebra, but is always separated from that face 
by a thin, flat pad, which, in the one specimen examined, was 
of tough, semi-cartilaginous tissue on the first two vertebrae, 
but, to all appearance, of true cartilage on the posterior ones. 
The pad or plate is, at its lower anterior end, continuous with, 
or connected with, the ligamentous tissue filling the median 
indentation in the base of the arch. It is also connected, 
at its lateral edge, by tendinous tissue, extending downward 
and backward along the lateral surface of the vertebra next 
posterior to the arch, with the intermuscular septum of that 
vertebra. 
The intermuscular septum on each vertebra runs from the rib 
of that vertebra directly upward toward the top of the vertebral 
body, where it turns sharply backward onto and across the 
lower, or lower and posterior, end of the dorsal arch that lies 
next behind that vertebra. It then runs in a nearly horizontal 
direction across the lower ends of the two dorsal arches next 
posterior to that arch, onto the third posterior arch. There it 
turns upward and backward along that arch, and onto the pro- 
cessus spinosus of the arch. At the distal end of the spine it 
turns sharply forward and upward, and reaches the dorsal sur- 
face of the body about opposite the vertebra to which it belongs. 
The angle formed where the septum first turns backward from 
its own vertebra, onto and across the dorsal arch next posterior 
to that vertebra, is much sharper on the anterior of the six verte- 
brae than on the posterior ones. It is at this angle that each 
septum receives the tendinous formation from the semi-carti- 
laginous pad that lies between its vertebra and the dorsal arch 
that lies next anterior to that vertebra. 
In larvae from 20 mm. to 50 mm. in length, the six vertebral 
processes of the adult, above described, are found as relatively 
large blocks of cartilage, three on each side of each vertebra, 
