1922.] 



S. L. Hopa : Fish of Mountain Torrents. 



39 



The muscles controlling the movement of the pectoral fin 

 (figs. 2, 3) in Glyptothorax are also interesting. Besides the abductor 



..J. 



■-n. 



Text-fig. 3. — Ventral view of the pectoral girdle in Glyptothorax madraspata- 



nus. 

 a = interclavicle : b = interclavicular ridge ; c = clavicle ; d = pectoral spine; 

 e = pectoral fin rays ; f = groove for the attachment of abductor muscles ; g = 

 groove in the cubito-humeral process ; h = abductor muscles ; I, 2 and 4 refer to the 

 muscles of the pectoral spine. 



and the adductor systems, there are four special muscles to move the 

 spine. Muscle 1 arises from the anterior grooved and thickened 

 border of the clavicle and also from along its posterior border near 

 the base of the interclavicular ridge against the sides. Its action 

 is to pull the spine towards the body and fold the rays. Muscle 2 

 takes its origin from the anterior border of the clavicle, further 

 forward than muscle 1. In its course, it passes underneath muscle 

 1 and its function is that of expanding the fin. Muscle 3 is very 

 extensive and fan-shaped. It arises along the whole of the surface 

 of the clavicle and the interclavicle on the dorsal side and in its 

 course passes through a bony canal. Its action is the same as 

 that of muscle 2. Muscle 4 is very strong and passes through a 

 passage in the bone. The muscle takes a curved course and its 

 action is somewhat like that of a rope passing over a pully. Its 

 function is that of folding the fin. It arises from the grooved and 

 thickened posterior border of the clavicle. 



The actions of the various muscles were studied by moving 

 the muscles and by watching their effect upon the fin. It is clear 

 that muscles 1 and 4 are stronger than 2 and 3, because it is in 

 the action of folding of the fin that the adhesive function of the 

 outer raj's is involved. In those species of Glyptothorax in which 

 the adhesive apparatus is present on the under surface of the pec- 

 toral spine, muscle 1 is the better developed. 



