251 
in the formation of the brachial plexus. — The ganglia of these nerves 
lie in a very small Saccus paravertebralis which does not com- 
municate with the cranial cavity as in Cyprinus, and inded can hardly 
be said to communicate with the Atrium sinusimparis, to such 
an extent is the apertura externa atrii closed by a thickened 
cushion of dura mater against which the spoonshaped process of the 
stapes rests, and through which the tendon connecting that bone with 
the incus passes. 
Although the 211 and 39 nerve emerge from the neural canal so 
near each other, their origin from the spinal cord is by no means so 
close. The fact that the 2°4 nerve especially the ventral root emerges 
so far back is due to the formation of the Atrium sinus imparis. 
The air-bladder. 
As in Silurus the air-bladder of the Cat-fish is subdivided by a 
median vertical partition for the hinder 2/3”% of its length. — The en- 
trance of each subdivision into the anterior undivided part is narrowed 
by a flattened vertical pillar, the dorsal edge of which is attached to the 
side of the body of the 5 vertebra, and to the ventral surface of the 
transverse process of the 4h. Apart from these pillars the anterior part 
alone of the air-bladder is attached to the vertebral column. In addi- 
tion to the two lines of attachment noted above (the posterior border 
of the body of the 3" vertebra and the thick part of the 4 trans- 
verse process), the dorso-median part of the tunica externa is firmly 
bound down over the bodies of the 4'° and 5tt vertebrae, and to a knob 
on the anterior end of an oblique ossification which passes backwards 
and outwards to become coalesced with the ventral surface of the 4% 
transverse process. ‘This ossification represents the line of strain in 
the movements of the malleus, for the knob occupies the concavity of 
the sickle shaped portion of that bone to which the fibres of the ventral 
and lateral parts of the tunica externa in this region converge. The 
hinge between the sickle shaped end of the malleus and the knob is 
formed by a ligament with tendinous lustre. From the mode of attach- 
ment of the air-bladder to the malleus, the sickle-shaped end of that 
bone is pulled away from the vertebral column by distension of the 
bladder, with a resulting inward movement of the anterior end of the 
malleus and of the stapes and a propulsion of the perilymph towards 
the labyrinth. 
The Labyrinth. 
With Nusbaum I find a transverse Ductus connecting the 
Sacculi and an impair Sinus endolymphaticus projecting from 
that into the Cavum sinus imparis. The sinus is pyriform in 
shape and extremely thin walled. I have not as yet succeeded in find- 
