No. 468.] MUSCLES OF ACANTHIAS AND RATA. 903 
lateral part of the labyrinth region of the cranium. Its fibers 
run obliquely forward and outward, forming the posterior wall 
of the spiracle, while the large lateralis nerve penetrates the 
middle of the muscle in order to reach the region of the fin. 
The muscle is inserted upon the hyomandibula, the line of 
insertion beginning behind that of the first dorsal constrictor 
and extending the length of the rest of the cartilage. This 
muscle has become differentiated from the rest of the con- 
strictor system and is only used to raise the hyomandibula. 
The other more lateral and posterior portion of the second 
dorsal constrictor (Csd 2) is associated with the others of the 
series. Its fibers are entirely distinct from those of the levator 
hyomandibularis and arise from the tendon separating the second ; 
and third constrictors. This tendon is not so extensive as the 
succeeding and does not extend laterally to the horizontal tendon 
which is correspondingly interrupted opposite this point. 
The remaining dorsal constrictors (Csd 3-7) are practically 
alike. Each arises from the tendon between itself and the next 
following muscle and is inserted on the tendon in front. The 
seventh forms an exception in that it is smaller than the others, 
and its fibers are not parallel to the main axis of the body, but 
converge to the point of origin upon the shoulder girdle. The 
intermuscular tendons incline more and more from the trans- 
verse direction as we go farther back, and, as the muscles 
extend to the horizontal tendon, they bend downward at the 
lateral margin in order to reach it. A few of the fibers of 
(Csd 3) are inserted in a strong tendon (F 3) which extends for- 
ward from the intermuscular tendon between constrictors 2 and 
3, ventral to all the adductors of the jaws, to be inserted on the 
skull and surrounding tissue lateral to the nostrils. 
The ventral constrictors (Fig. 3, Csv) are likewise seven in 
number. The first, instead of forming a broad sheet as in 
Acanthias, is divided into two portions, an anterior part, which 
extends from one mandibular half to the other just behind the 
symphysis, and a posterior portion. The anterior portion is not 
constantly present ; I failed to find it in one specimen. 
The posterior part of the first ventral constrictor is a flat fan- 
shaped muscle which arises in connection with the depressor 
