No. 468] MUSCLES OF ACANTHIAS AND RAIA. gol 
Rata. 
In removing the skin from the skate, there is less connective 
tissue than in Acanthias, the constrictors are not so conspicuous, 
and more muscles occur, as for instance those which control the 
rostrum. The muscles, too, have been altered in relative size 
and position in accordance with the modification of form in this 
extreme type, but the same general relations are easily followed. 
The constrictors have increased in number to seven, and, 
associated with the extreme flattening of the branchial region, 
the dorsal and ventral constrictors are not continuous as in 
Acanthias, but are distinct, being separated at the lateral part 
of the branchial region by what Tiesing has called the horizon- 
tal tendon. This tendon starts from the lateral end of the hyo- 
mandibular cartilage, and running along the anterior surface of 
the gill region, connects with the propterygium and continues 
back in the lateral branchial region, affording insertion to both 
dorsal and ventral constrictors. Since the gill slits lie wholly 
upon the ventral surface, the ventral constrictors in turn have 
divided into median and lateral portions, the line of division 
occurring at the median ends of the gill clefts (Fig. 6). 
Dorsal Constrictors.— The first dorsal constrictor (Fig. 6, 
Csd I) takes its origin from the lateral labyrinth region of the 
skull, ventral and posterior to the postorbital process, and is 
continuous posteriorly with the levator maxillae superioris, these 
two muscles, as in Acanthias, having a common origin. The 
fibers run forward, curving laterally along the anterior margin 
of the spiracle, and are inserted on the dorsal surface of the 
hyomandibula, a short distance from its anterior end. A sheet 
of fascia (7) to be described later, has a part of its origin from 
this muscle near its insertion; in part it also arises from the 
posterior margin of the spiracle. 
The second dorsal constrictor (Cs4 2) is 
ferentiated than in Acanthias, having developed into distinct 
muscles with different functions — an anterior levator hyoman- 
dibularis and a posterior portion which agrees with the other 
constrictors in position and shape. 
The levator hyomandibularis (Z Hm) arises from the postero- 
larger and more dif- 
