ON THE ANATOMY OP FISHES. 
U9 
the transverse processes of the fourth and fifth vertebrae on each side combine to 
form an extensive wing-like outgrowth with a decurved anterior margin wliich closely 
envelopes the dorsal wall of the anterior compartment of the air-bladder, and at the 
same time buttresses the anterior wall (fig. 35, t.pM. and 
The air-bladder itself is more distinctly cordate than in Platystoma, and its walls 
are extremely thin (a.b.). The ventral wall of the anterior chamber is almost com- 
pletely invested by powerful compressor muscles. A tensor tripodis is also present 
on each side, and has the same origin and insertion as in Platystoma. No antero- 
lateral or other csecal appendages are present. Two rudimentary secondary transverse 
septa only are present in each lateral compartment {t.s.'). In the general structure 
of the walls of the anterior chamber, and in their relations and attachments to the 
transverse processes of the fourth vertebra and to the tripodes Piramutana differs 
in no essential respect from Platystoma. The lateral walls of the anterior chamber 
are in close and extensive contact with the lateral cutaneous areas. 
Piramutana Blochii. 
Under the name of Pseudariodes clarias (Bleek.) S5kensen (36) figures and 
describes the air-bladder of this species. His figure {l.c., Plate 3, fig. 45) shows the 
left compressor muscle and on the right side the cavity of the bladder and its 
internal septa. 
Piratinga Jilamentosa. 
Johannes Muller (28) has figured and described the air-bladder of this Siluroid 
under the name of Pimelodus Jilamentosa (Lichtenst.). The organ is said to consist 
of two entirely distinct flat sacs lying one behind the other and both cellular through- 
out. The ductus pneumaticus is connected with the anterior sac. The posterior sac 
is said not to contain the usual central cavity, the whole of the interior being occupied 
by small air-cells. Later on (p. 141) in alluding to the same species, Muller says, 
“ in which there is a second cellular air-bladder, without any union with the first, 
without connecting duct, and without communication with a respirable medium.” 
Pimelodus maculatus. 
In this species the air-bladder differs but little from that of Piramutana, and the 
same may be said of the skeletal modifications. 
The air-bladder has rather thick walls, and, in addition to the primary transverse 
and longitudinal septa, there is a rudiment of a single secondary transverse septum in 
each lateral compartment. The lateral portions of the primary transverse septum 
are nearly vertical, and have their dorsal margins attached to the ventral surfaces of 
the transverse processes of the sixth vertebra, but, as they approach the median line, 
