VISCERAL ARCHES OF THE GNATHOSTOME FISHES. 331 
is not so attached, in my specimens, to the posterior wall of 
the next anterior pouch. The liyal constrictor and its related 
branchial rays are but loosely attached to the anterior wall 
of the first gill-pouch, this apparently being due to this 
muscle being a thicker and stronger muscle than the branchial 
ones. 
On the external surface of each wall of each gill-pouch 
there are tall and narrow U-shaped lines which mark the 
lines of attachment of the branchial lamellae on the internal 
surfaces of those walls. The loops on the posterior wall of 
the pouch lie against the anterior surface of the constrictor 
next posterior to the pouch, and, on that surface of that 
constrictor, and extending from the outer (distal) ends of 
the loops to the outer edge of the depression that lodges the 
gill-pouch, there are, dorsal and ventral to the gill-openings, 
several strands of a tissue that is largely fibrous, but that 
shows, under the microscope, certain transverse striae. These 
strands are radially disposed, as are the branchial lamellae; 
they cross the fibres of the constrictor at right angles, and 
they are closely attached to the anterior surface of that 
muscle. Their position suggests both the supporting rods 
of the branchial filaments in the Teleostomi and the radially 
arranged muscles related to those rods (Allis, 1903), but it 
seems improbable that they represent the beginnings of the 
formation of either of them. On the posterior wall of each 
gill-pouch, opposite the dorsal one of these two series of 
fibro-muscular strands, there are one or two flat muscle 
bauds which lie approximately parallel to the fibr.ous strands, 
but closely attached to the wall of the pouch instead of !o 
the anterior surface of the constrictor. Distally, these bands 
pass over the outer edge of the pouch, close to the dorsal 
end of its external opening, and, turning ventrally, join, 
near its distal edge, the constrictor that lies along the 
anterior wall of the pouch. Ventral to the gill-openings 
similar strands are found, but they here lie upon the internal 
(posterior) surface of the constrictor next anterior to the 
puuch, close against the outer edge of the pouch, instead of 
