904 THE AMERICAN NATURALIST. [Vor. XXXIX. 
rostri (to be described later) in the fascia covering the coraco- 
arcualis communis, and is inserted upon the mandible at about 
the center of its posterior edge. This part of this ventral con- 
strictor thus forms a distinct depressor mandibuli (Dm). Only 
the anterior edge of the origin of this muscle can be seen until 
the depressor rostri (Fig. 15, Dr) is removed, but the method of 
description necessitates its mention here. 
The second ventral constrictor is likewise much modified from 
the condition in Acanthias, being divided into an anterior depres- 
sor hyomandibularis (D//m) and a posterior second ventral con- 
strictor proper (Csv 2). 
The depressor hyomandibularis has its origin in the fascia 
overlying (ventral to) the coraco-hyoideus, the fascia connecting 
the depressors of the two sides dorsal to the coraco-mandibu- 
laris. The general course of the muscle is transverse to the 
longitudinal axis of the body. The fibers converge from a 
broad flat origin to a cylindrical muscle which then runs dor- 
sally and becomes inserted upon the posterior end of the ventral 
edge of the hyomandibula and upon the horizontal tendon. The 
posterior portion of the second ventral constrictor has its origin 
in part in the tendon (less developed than the others) separating 
it from the third ventral constrictor, while the more lateral fibers 
are continuous with those of the third constrictor, there being 
no aponeurosis between them. The fibers run forward, con- 
verging from either side toward their insertion on the horizontal 
tendon. ; 
Each of the remaining ventral constrictors (Csv 3—Csv 7) is 
composed of two parts, a large median and a smaller lateral por- 
tion, the muscle becoming smaller toward the lower limits of 
the gill region. The tendons separating the constrictors (the 
first two are united medially) run obliquely outward and back- 
ward to the median ends of the gill slits and then turn abruptly 
and pass to the middle of the gill slit behind, so that this por- 
tion of the tendon serves to separate the median from the lateral 
parts of the muscle. 
The origin of the median portion of the seventh ventral con- 
strictor is from the fascia covering the ventral edge of the 
coraco-branchialis. The other muscles arise from the tendon 
