Ps 
“ 
THE OSTEOLOGY OF AMIURUS CATUS. 295 
jecting process from that plate. The fifth is of the normal type, all 
its parts being present, but its body is united anteriorly with that of 
the fourth. The bodies of the 2nd-5th are deeply grooved below for 
the reception of the aorta. 
The bodies of the succeeding vertebrae as far back as the com- 
mencement of the tail fin are all similar in appearance. They are 
of the usual piscine amphicelous type, but they are very much 
flattened at the centre of their length from above downwards, and a 
strong longitudinal ridge extends along the lateral surface of each, 
increasing the appearance of flattening. In the adult the bodies, as 
well as the arches, are thoroughly ossified, no notachord remaining 
in the centre of the bodies. In a stage incompletely ossitied it may 
be seen that the notachord is contracted very much vertebrally, ex- 
panding rather suddenly as one approaches either extremity of the 
body, and resuming its full uncontracted size. The lateral ridge 
seems to be formed by an extension of the ossification into the adher- 
ent connective tissue along the lateral line of the column. On the 
upper and lower surfaces of each centrum, on either side of the 
middle line, is a ridge, so that viewed laterally the vertebre do not 
appear extraordinarily flattened. Posteriorly in each vertebra, 7. ¢., 
between the attachment of successive arches, these ridges increase in 
height, thus forming a protection for the spinal cord or aorta between 
the arches. 3 
The arches are completely ossified, and are firmly anchylosed with 
the bodies. They unite with the anterior portions of the bodies 
above and below, enclosing in either case the spinal cord or the 
aorta. In the more anterior dorsal arches the anterior elevations of 
the dorsal longitudinal ridges of the centra articulate with the 
posterior border of the preceding arches, but posteriorly no such 
articulations obtain. All the dorsal arches, and the hemal arches 
also in the tail region, are surmounted with long backwardly directed 
spinous processes ; those of the 5th-9th dorsal vertebrz inclusive being 
bifid for the reception of the interspinalia of the dorsal fin. The 
majority of the vertebre of the trunk region have their lower 
arches projecting at right angles from the centrum, forming the 
transverse processes ; with the 6th-14th of these ribs (ossifications of 
intermuscular septa) articulate, the upper surfaces of their proximal 
portions being in contact with the under surface of the distal ex- 
tremities of the transverse processes. The last two vertebre of the 
