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ascending process which unlike the others contributes to the formation 
of the wall of the neural canal. 
The Claustrum is triangular in shape and fits with its apex point- 
ing downwards and backwards into the angle between the anterior 
and ascending processes of the stapes. It has no relation to the 
Atrium sinus imparis as in Cyprus, but contributes to the for- 
mation of the lateral-wall of the neural canal in this region. In young 
cat-fish of 3—4cm length the Claustra are almost entirely cartilaginous 
and in horizontal sections through such are to be recognized as distinct 
rods between the roof.of the foramen magnum and the cartilage cover- 
ing the spinal cord in the region of the second and third vertebrae.f 
The incus of the adult is similar as to that in S. glanis, but in 
‘young forms is a slender spicule the anterior end of which is lodged in 
the ligament between malleus and stapes, while the posterior end 
stretches back towards the upper surface of the 2° vertebra. Like the 
anterior and ascending processes of the Stapes it is not preformed in 
cartilage and I have not been able to trace it back so far as the carti- 
laginous patch in the body of the 2% vertebra to which as modified 
neural arch it belongs. The incus increases in size in the adult by the 
ossification of the ligament between malleus and stapes. I am able 
here to confirm Baudelot’s observation that the incus in Catostomus 
is slender and style-like and has similarly lost all connection with the 
body of the 224 vertebra — In form it resembles that of the young cat- 
fish, and, as might be expected from the greater richness in cartilage 
in this region of the vertebral column of the Cyprinoids, does not be- 
come entirely ossified except in the adult. 
The malleus is developed in two parts, the anterior of which (the 
transverse process of the 3” vertebra) only becomes connected with 
the posterior sickle-shaped part in the adult. The latter is in fact 
nothing but an ossification in the tunica externa of the air bladder. — 
There is never any trace of cartilage in the malleus except just at its 
junction with the body of the 3” vertebra. 
The Vertebrae concerned. 
The 6 is the first rib-bearing vertebra. The vertebrae in front 
of that have no ribs, but only rib - bearing pedicles, »Basal-Stumpfec, 
which I shall call here Transverse Processes. 
The 15° vertebra has very rudimentary transverse processes, its 
body bears on the dorsal surfaces two articular cavities for the Sta- 
pedes, while on the ventral surface are accessory articulating lamellae 
which fit between similar processes from the combined 2°¢and 3"¢ Ver- 
tebrae. As described above the neural arches are converted into the 
stapedes, and the spinous process into the Claustra. 
