No.3.] MUSCLES AND NERVES IN AMIA CALVA. 671 
portion of the dorsal surface of the third infrapharyngobran- 
chial, runs directly across the middle line of the head, ventral 
to the retractor, and is apparently simply an anterior portion 
of the constrictor of the pharynx, with which it is continuous. 
c. Retractor Arcuum Branchialium Dorsalis. 
‘hiss muscle (Kaba, Figs: 62,53) and 62, Pls. XoXxOChy 
and XXXVII) is a large and stout one arising from the 
sides of the bodies of the third and fourth vertebrae. It runs 
directly forward along the under surface of the spinal column 
and of the posterior portion of the skull, and is inserted, on 
each side of the head, on the median portion of the dorsal 
surface of the anterior end of the third infrapharyngobranchial, 
its lateral fibres sometimes turning outward and then backward 
around the front edge of the levator arc. branch. int. post., 
ventral to the anterior transversus, to be inserted with the latter 
muscle on the outer, anterior edge of the infrapharyngobranchial. 
The two halves of the muscle are, in its anterior part, more or 
less continuous, and the arrangement of the two differs in 
different specimens. Some of the fibres of the muscle arising 
from one side of the spinal column may cross the middle line 
of the head and be inserted on the infrapharyngobranchial of 
the opposite side. The muscle lies immediately ventral to the 
dorsal aorta, but dorsal to the trunk of the united efferent 
arteries of the third, fourth, and fifth arches on each side, which 
trunks unite in the middle line to form a common trunk, 
which runs upward through the muscle at about the middle 
of its length to join the aorta. 
4. Adductores Arcuum Branchialium. 
There are two of these muscles, one the adductor of the 
fourth arch, the other that of the fifth (Figs. 48 and 56, 
Pls. XXXIII and XXXV). The former (Aad./V) arises from 
the under surface of the distal cartilaginous cap of the fourth 
epibranchial and from the under surface of the adjoining bony 
portion of the piece, and is inserted on the entire dorsal sur- 
face of the triangular cartilaginous cap of the fourth cerato- 
