68 THE VOYAGE OF H.M.S. CHALLENGER. 



Relations. — The muscle is in part concealed on the outer side by the cruro-coccygeus, 

 which lies parallel with and separates it from the origin of the semi-tendinosus. Its 

 inner surface is in contact with the abdominal viscera. 



Nerve supply. — Branches from the anterior divisions of the coccygeal nerves. 



Remarks. — I have experienced considerable difficulty with regard to the synonjony 

 of this muscle. This arises from the fact that in the majority of birds there are more 

 than one abductor of the tail, and the descriptions of the various anatomists quoted are 

 not so precise as one could wish. I have attempted to come to a correct decision as to 

 the synonyms, but that I entertain doubts with regard to certain of these is indicated 

 by the insertion of points of interrogation after them. 



(e) Muscles inserted into the Eibs. 

 1. Diaphragm. 



Attachments. — The diaphragm is a thin fleshy plate, which arises by means of six 

 distinct dio-itations from the inner or thoracic surfaces of the second to the seventh 

 vertebral ribs inclusive, close to the articulations of these with the corresponding sternal 

 segments. The fibres pass upwards, and are inserted into the lower or cardiac surface of 

 the luns; of the same side. 



Action. — This muscle acting upon the lung assists in the expansion of that organ. 



Nerve supply (?) 



Variations. — In Spheniscus mendiculus the origin of the diaphragm is confined to 

 four ribs, namely, to the second, third, fourth, and fifth. In Spheniscus demersus, on the 

 other hand, the muscle is larger than in other species, and is attached to all the vertebral 

 ribs, with the exception of the first. 



2. Tnangidaris sterni. 



Der innere oder drdeckige Brustmuskel, Tiedemann, p. 300, Xo. 4. 



Der Erheber der Rippenfortsdtze, Merrem. 



Tria7igidaire du sternum, Cuvier, voL i. p. 219. 



Muscle No. 4, Meckel, vol. vi p. 17. 



Triangularis sterni, Selenka, vol. vi. p. 104, No. 29. 



Triangulaire du sternum, Gervais and Alix, p. 1 6. 



Attachments. — This muscle arises by means of a stout tendon from the thoracic 

 surface of the costal process of the sternum. Its fibres pass horizontally backwards, and 

 are inserted by means of distinct muscular slips into the inner surfaces of the first four 

 sternal ribs. The most anterior slip is attached to its rib at some distance from the 

 sternum, while the succeeding slips approach successively nearer to that bone. 



