892 THE AMERICAN NATURALIST. (Vor. XXXIX. 
4. Ventral longitudinal muscles. 
Each of these in turn contains several muscles which are capa- 
ble of arrangement under subordinate headings. In the follow- 
ing account, the muscles of one of the major divisions will be 
described for Acanthias, and then the corresponding muscles for 
Raia. 
SUPERFICIAL CIRCULAR MUSCLES. 
Of these there are seven groups :— 
I. Superficial constrictors; a, dorsal; 4, ventral. 
2. Interbranchiales (lying between the walls of the gill 
clefts). 
3. Levator maxilla superioris (raising the upper jaw). 
4. Trapezius (raising the shoulder girdle and drawing it for- 
ward). 
5. Levator labialis superioris (raises the upper lip), 
6. Levator rostri (raises the rostrum). In Raia only. 
7. Depressor rostri (depresses the rostrum). In Raia only. 
Superficial Constrictors. 
Acanthias. 
The superficial constrictors are the most external of the mus- 
cles which cover the gill pouches and form the surface of ‘the 
region of the ‘neck.’ They may be divided, from position, into 
dorsal and ventral constrictors and are six in number on either 
side. Between them the five gill slits are placed, the first lying 
between the second and third, the fifth gill slit occurring behind 
the sixth constrictor (Figs. 1, 2). The gill slits are slit-like in 
character, about 18 mm. in extent, and are vertical in position, 
located near the ventral portion of the side of the body. 
Dorsal Constrictors — The first and most anterior dorsal con- 
strictor (Fig. 2, Csd 7) takes its origin from the lateral surface 
of the cranium just below the posterior end of the dorso-lateral 
ridge. Its point of origin is not separated from that of the 
levator maxillae superioris, to be described below. Its fibers run 
ventrally and forward, curving around the anterior wall of the 
