916 THE AMERICAN NATURALIST. | (VoL. XXXIX. 
It may be a question whether the interbranchiales, the inter- 
arcuales, and the adductores (next to be described) do not form 
a system of deep as opposed to the superficial constrictors. 
Each contributes toward the constriction of the whole branchial 
region, and, with the exception of the largest mandibular adduc- 
tor, each lies beneath the more superficial system. 
ADDUCTORES. 
The adductor muscles draw together the ventral portions of 
each visceral arch. In the case of the mandibular arch they 
close the mouth, while in the gill arches they occur at the lateral 
hinge and approximate the ceratobranchial and epibranchial por- 

FIG. 12, — Anterior side of interbranchial muscle of Raia. Aab, adductor arcus branchialis ; 
Intr, interbranchiales. 
tions of each. The adductors of the first (mandibular) arch are 
enormously developed in correlation with the use of these parts, 
while those of the gill arches are very small. In Acanthias the 
adductors are much simpler than in Raia. 
Adductores Mandibulares. 
Acanthias. 
very strong tendinous envelope. Its fibers arise from the quad- 
rate region of the upper jaw, and are attached to the entire 
lateral surface as well as to the medial surface of the muscle 
process on its dorsal margin. The course of the fibers is down- 
The mandibular adductor (Figs. 1, 2, 13, 14, Am) has a 
