No. 468.] MUSCLES OF ACANTHIAS AND RAIA. 909 
postorbital process. It is larger than the first dorsal constrictor 
and fills the: entire bay back of the postorbital process. The 
fibers extend anteriorly and ventrally to their insertion on the 
dorsal margin of the palatal process of the upper jaw, just ante- 
rior to the attachment of the first dorsal constrictor. In fact 
the only distinction that can be drawn is that in the levator the 
fibers go directly to the jaw while those of the first dorsal con- 
strictor curve around the anterior margin of the spiracle. 
Raia. 
In the skate the levator of the upper jaw (Figs. 3, 6) is com- 
posed of a thick dorsal and a thinner ventral layer, the two 
united at their point of insertion. The thicker layer (Lms) 
arises from the side of the skull, just ventral to the postorbital 
process, and its fibers run almost straight forward, then dorsal 
and backward in front of the oral cavity to their insertion on 
the upper jaw. The thinner and more ventral layer (Zu) arises 
‘just below and behind the facial foramen whence its fibers run 
forward, laterally, and backward to unite with the dorsal layer. 
This course involves a strong lateral bend from which a strip of 
fascia extends to the hyomandibular cartilage (Fig. 6). Some of 
the more ventral fibers are inserted in the membranous wall of 
the roof of the mouth. 
Tiesing maintains that the levator maxillae superioris is only 
a deeper part of the first dorsal constrictor,— a view rendered 
very probable from the relations in Acanthias in which the con- 
ditions are the more primitive. It is very similar to a constric- 
tor in origin and function, although differing widely.in form. 
Trapezius. 
Acanthias. 
The trapezius (Figs. 2, 7, 8, H, Tr) has its origin in fascia 
covering the sides of the dorsal longitudinal muscles. Its fibers 
arise from a straight line extending from the posterior end of the 
cranium to the dorsal part of the shoulder girdle, although the 
