406 
EDWARD PHELPS ALLIS. 
of the figure the ventral portions of the constrictores of the first three 
branohial arches have been cutaway up to the line of the extrabranch ial 
of the arch, and on the right-hand side of the figure the ventro-posterior 
portions of the gill pouches have been cut away so as to expose the 
underlying constrictor of the next posterior arch. In the fourth 
branchial arch a piece has been cut out of the constrictor of the arch 
( Cs . 6 ) so as to expose the fifth gill pouch. The musculi coracomandi- 
bularis, coracohyoideus, coracobranchialis I, and coracoarcualis have 
been cut through and removed. X 1§. 
PLATE 22. 
Fig. 5. — The same ; a still deeper dissection. The ceratohyal and the 
extrabranchial of the first branchial arch both removed on the right- 
hand side of the figure. X 1| 
Fig. 6. — The same ; a still deeper dissection. The extrabranchial of 
the second branchial arch also removed on the right-hand side of the 
figure. X 1L 
Fig. 7. — Lateral view of the branchial region of the same. The con- 
strictores superficiales of the hyal and first three branchial arches, and 
the four related gill-pouches removed, but the cut dorsal ends of the 
extrabranchials of the first three branchial arches left in place. X 2. 
Fig. 8. — Lateral view of the head of a 43-cm. Mustelus. The skin 
removed so as to expose the constrictores superficiales of the hyal and 
branchial arches. X 2. 
Fig. 9. — The same. The continuous sheet formed by the constrictores 
superficiales has been cut along its dorsal edge, and those fibres of 
each musculus interbranchialis that are inserted in the related linear 
aponeurosis ha*e also been cut close to their insertion on that aponeu- 
rosis, and the entire muscle sheet, excepting the distal portion of the 
constrictor of the fourth arch (Cs. 6 ), then turned downward to the level 
of the middle line of the gill openings. X 2. 
Fig. 10.— Lateral view of the constrictor and interbranchialis muscles 
of the third branchial arch of Mustelus. Dorsally, the continuous 
muscle-sheet formed by the constrictores superficiales has been cut 
along the line of the linear aponeurosis related to the arch, and also 
slightly posterior to that aponeurosis. Yentrally, the muscle-sheet has 
been cut immediately anterior to the line where the ventral portion of 
the constrictor of the arch (Cs. 5 ) joins it, and also slightly posterior to 
that line. X 2§ 
