534 



LOUISE SMITH 



of about ten more or less complete series of larvae I found a few- 

 sections that showed a definite, though narrow raphe (fig. 1, a) 

 and a few more, where careful focusing brought out a minute 

 division across the middle of w^hat otherwise appeared to be a 

 single fiber (fig. 1,6), but in the majority of cases the fibers were 

 quite unbroken across the midline (fig. 1, c). 



The geniohyoideus, a long, narrow muscle, arising from the 

 symphysis of the mandible, extends posteriorly at either side of 

 the midline and is inserted into the anterior edge of the lateral 

 projection of the second basibranchial. 



The thoracicohyoideus is very large and powerful. Its main 

 portion arises from the pectoral girdle and the whole segmental 

 trunk musculature, passes forward around the pericardial 



Fig. 1 Representative fibers of the M. intermandibularis drawn from a trans- 

 verse series. 



chamber, and is inserted into the whole dorsal surface of the 

 plate, the posterior end of the first basibranchial and proximal 

 end of the second epibranchial. In addition, a superficial slip 

 arises from a myocoimna opposite the proximal end of the third 

 epibranchial, and is inserted into the posterior edge of the lateral 

 projection of the second basibranchial. 



The ceratohyoideus externus, the largest of the intrinsic muscles 

 of the hyobranchial apparatus, arises from the middle of the 

 ventral surface of the ceratohyal along almost its entire length, 

 and curves around posterolaterally to be inserted, together with 

 a slip from the dorsal surface of the head, probably the levator 

 arcus primus, into the dorsal surface of the distal end of the first 

 epibranchial. 



The ceratohyoideus internus is very much smaller than the 

 externus and is entirely covered by it. It arises from the dorso- 



