6()8 



Dr. HARRIS H. WII.DEU, 



in a small dissectiag pan upon the stage of a dissecting microscope. 

 Carefully remove the integument from the external gills and prepare 

 the muscles beneath. 



These consist of a series of subcutaneous slips, destined to move 

 the external gills, and are possessed by all Perennibranclis. 



They may in all cases be divided into three groups, adductors, 

 levators and depressors, but the number and arrangement of the muscles 

 comprising these groups differ in the difterent genera and species. 

 The relations of these muscles in Siren may be made clear by refer- 

 ence to fig. 7 and may be given in tabulated form as follows : 



Origin 

 Superior extremity 

 epibranchale 2 



Adductor branchiae I 



of 



Adductor branchiae II 



[The function of an 

 adductor branchiae III 

 is supplied by the pro- 



coraco-branchialis] 

 Levator branchiae III 



Depressor branchiae I 



Superior extremity 

 epibranchiale 3 



Insertion 

 Posterior superior sur- 

 face of the 1*' external 

 gill 

 of Posterior superior sur- 

 face of the 2"** external 

 gill 



Depressor branchiae II 



Depressor branchiae III 



Superior extremity of 

 epibranchiale 2, beside 

 the origin of adductor 



branchiae I 

 Ventral half of the pos- 

 terior margin of epi- 

 branchiale 1 

 Ventral half of the pos- 

 terior margin of epi- 

 branchiale 2 

 Medial third of the pos- 

 terior margin of epi- 

 branchiale 3 



Anterior superior sur- 

 face of the 3'''* external 

 sill 



Posterior inferior sur- 

 face of the 1*' extei-nal 



gill 

 Posterior inferior sur- 

 face of the 2"'^ external 



gill 

 Posterior inferior sur- 

 face of the 3''' external 



gill 



Innervation. The entire 2"** external gill, including its muscles, 

 is supplied by a branch from the glossopharyngeus. The remainder 

 of this region receives nerve supply from several fine twigs which 

 come directly from the root of the vagus. 



15. Systems of the Pharyngeal constrictor and the laryns^eal 



muscles. 



For the best results in the preparation of these parts, the entire 

 thoracico-hyoideus, as well as the shoulder girdle, should be removed. 



