SKELETAL MUSCULATURE OP THE KING SALMON. 39 



LEVATORES ARCUUM BRANCHIALIUM. 



* This group consists of five diverging muscle slips which are subdivisions of one 

 thin broad sheet. The origin of the muscle sheet is on a line immediately ventral 

 to the origin of the middle portion of the adductor arcus palatini. At the origin the 

 sheet is continuous and its divisions spread out to their attachments somewhat like a 

 miniature fan. 



Fijth division. — This, the most posterior slip of the group, is a very slender muscle 

 arising from a point on the skull just in front of the foramen of the tenth ner\'e. The 

 fibers run posteriorly downward and backward to an attachment on the dorsal margin 

 of the flange of the fourth epibranchial. This muscle is about 2 to 2.5 cm. long, the 

 longest of the group. 



Fourth division. — A similar though slightly stouter muscle arises just in front of 

 the latter and is attached on the crest of the corresponding flange of the third epibran- 

 chial. 



Third division. — The next differentiated strip runs under the tendon of the fourth 

 division and the flange of the third arch and is attached to the dorsal end of the carti- 

 laginous rod corresponding to a fifth epibranchial. 



Second division. — The second division is attached on the flange of the second epi- 

 branchial. But a tiny slip of this muscle also runs to the dorsal surface of the pharyngo- 

 branchial of the third arch. 



First division. — The most anterior slip is attached superficially to the flange on 

 the first epibranchial. But its deeper fibers run to the pharyngobranchial of the second 

 arch. These fibers are only a few millimeters long. 



The points of attachment of the first, second, and third muscle slips are also com- 

 mon points of union for the connective tissue and septa covering the corresponding gill 

 clefts, i. e., the first muscle is opposite the angle of the second gill cleft, the second oppo- 

 site the third, and the fourth opposite the fourth. 



The pharyngobranchial attachments of the first and second divisions are apparently 

 the homologies of McMurrich's levatores intemi, while the five divisions described here 

 would be his extemi. 



INTERARCUALIS DORSAUS OBI^IQUUS, POSTERIOR. 



There are two obliqui interarcuales on the dorsal half of the branchial arch. The 

 most posterior dorsal oblique arises from the posterior dorsal surface of the third pharyngo- 

 branchial. The fibers run obUquely backward to an insertion on the anterior surface 

 of the flange of the fourth epibranchial. 



INTERARCUALIS DORSALIS OBLIQUUS, ANTERIOR. 



The second or anterior oblique arises from the second pharyngobranchial near 

 its union with the epibranchial. The fibers run obHquely outward to an insertion on 

 the anterior margin of the flange of the third epibranchial. 



ADDUCTOR ARCUUM BRANCHIALIUM, ANTERIOR. 



There are two dorsal adductor muscles, an anterior and a posterior. The anterior 

 adductor arises on the posterior surface of the fourth epibranchial plate and is inserted 

 into the dorsal surface of the distal end of the corresponding ceratobranchial. Its 

 contraction approximates the cerato and epibranchials of the fourth arch. 



