A Coutritiutioii to the Anatomy of Siren laeertina. Q^^'{ 



lu nervation. From Nervus lateralis inferior X, which runs 

 directly behind the muscle. 



13. Constrictor arciium branchiariim (tigs. 2, 7, c. a. b). 



Preparation. After the removal of the preceding muscle, the 

 constrictor will be plainly seen as a band lying inferiorly and posteri- 

 orly over the arches at the base of the external gills. This muscle 

 is attached in Siren only at the ends, and may either bo lifted from 

 the subjacent tissue , divided in the middle and retiexed , oi- divided 

 near either extremity. If divided at the posterior end, notice must 

 first bo taken of its nerve supply from the vagus. 



Attachments. The anterior attachment is to the inner third 

 of epibranchiale 1, from which the muscle extends around the gills to 

 epibranchiale 4, into the inner half of which it is inserted. 



Innervation. It is supplied by fibres from the Ramus recur- 

 rens vagi which will be seen running superficially over the posterior 

 portion of the muscle. 



13. Protractor arciis ultimi (figs. 7, p.a.u.). 



Preparation. This muscle may, without farther preparation, 

 be seen extending along the posterior border of the last gill arch. 



Origin. The posterior border of cerato-branchiale 2. 



Insertion. The posterior border of epibranchiale 4. 



Innervation. The Ramus recurrens vagi has two principal 

 branches, each of which supplies a portion of this muscle. This may 

 best be seen upon the side from which the thoracico - hyoideus has 

 not been removed. Draw back the lateral margin of the hitter muscle 

 and the nerve and its branches will be seen resting upon the deep- 

 lying dorso-trachealis. In order to see this well, it may be necessary 

 to remove the procoraco-branchialis and also a part of the aortic 

 branches which lie in this region. 



14. Intrinsic muscles of tlie external gills (fig. 7). 

 After the removal of all the preceding muscles, the four epi- 

 branchials together with the external gills are conveniently removed 

 for more careful examination. This is done by cutting through the 

 articulations between the cerato-branchials and the epibranchials, and 

 severing the pharyngeal mucous membrane. Notice that a small 

 muscle , the hyo-trachealis , is cut through near its origin from epi- 

 branchiale 4. When separated, the entire apparatus may be prepared 



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