À Contribution to llie Anatomy of Siren lacertina. 660 



of cerato - branchiale 1. 3) To the posterior termination of 

 basibranchiale 1, underneath the 2"'^ basibranchial. 



b) Adductor es a reu uni. The paired sUps previously severed 

 from the main muscle may now be farther traced to their 

 attachment at about the middle of epibranchiale 2 and 3 

 respectively ; 



c) Omo-hyoideus. This muscular slip, anteriorly blended 

 with thoracico - hyoideus arises from the under surface of the 

 cartilaginous shoulder girdle, near the base of the procoracoid. 

 With regard to the homology of this muscle with the omo- 

 hyoideus, the following facts may be of interest: 



a) Its innervation is from N. hypoglossus. 

 ß) Its topographical position is certainly similar. 

 /) Albrecht states that the sterno-hyoideus of Perennibranchs 

 is the homologue of the omozomo - hyoideus of fish, and 

 describes this partially differentiated slip in Menoh'anchus 

 as the omo-hyoideus although he failed to find it in 

 Siren. 

 S) Gegerbaur states that in the human subject „eine Ver- 

 schmelzung des vorderen Bauches (des betreffenden Muskels) 

 mit dem sterno-hyoideus ist gleichfalls nicht selten", a con- 

 dition precisely like that of Siren. 

 Innervation. The main portion of this system is supplied 

 by the hypoglossal (= Nervi cervicales l-|-2) which soon after their 

 passage through the dorsal muscles curve backwards, running parallel 

 with Ramus recurrens vagi, and while lying upon the thoracico-hyo- 

 ideus supply it with numerous fine twigs, the omo-hyoideus receiving 

 a part of this supply. 



The nerve is readily seen lying upon the side of the muscle, if 

 one draws the muscle a little inwards. 



With regard to the innervation of the adductores arcuum, I have 

 succeeded no better than the previous investigators, but there is no 

 reason for doubting that they receive nerve-supply from the same 

 source as the rest of the mass, from which they are not fully se- 

 parated. 



10. Levatores arcnum (figs. 2, 6 I a. i, ^, .'i, 4). 



Preparation. These are four muscular bands lying dorsal 

 to the external gills. The first is somewhat separated from the others 



Zool. Jrihrt). IV. AWh. f. Morph. ^.j. 



