EEPORT ON THE SPHENISCID^. 207 



muscles pass forwards, and converging come into contact about the middle in length 

 of the neck. From this point forwards they diverge, and each (after winding round 

 the lateral surface of the trachea) is inserted into the superior and lateral surfaces of the 

 thyroid cartilage close to its posterior border. 



Action. — ^This muscle retracts the thyroid cartilage, and indirectly the hyoid bone, 

 and approximates them to the clavicle. 



Relations. — The muscles at their origin are almost inseparable from the superjacent 

 fibres of the cutaneous muscle of the neck. In the terminal part of their course the 

 muscles lie in contact with the trachea. 



Nerve supply {X) 



Variations. — In three species of Spheniscus, namely — Si^lieniscus magellaniciis, 

 Spheniscus demersus, and Spheniscus mendiculus, I found this muscle prolonged forwards 

 to the great cornu of the hyoid bone, to the apohyal element of which it took a distinct 

 attachment. Neither in Spheniscus minor nor in any species of the other genera which 

 I dissected was this the case. 



2. Sterno-trachealis muscle. 



Les laringiens inferieura et exfernes, Vicq d'Azyr, 1773, p. 581, No. 3. 

 Brustheiii-Luftr'dliren Muskel, Tiedemann, \). 666, No. 1. 

 Sterno-tracheene, Cuvier, vol. iv. p. 466. 

 Sterno-trachealis, Meckel, vol. x. p. 340. 

 Sterno-tracheen, Gervais and Alix, p. 17. 



Attachments. — The sterno-tracheal muscle arises from the deeper or thoracic surface 

 of the costal process of the sternum. The fibres form a riband-like muscle, which passing 

 forwards, gains the lateral aspect of the trachea Ij inches in front of the bifurcation 

 of that tube. Its anterior fibres are inserted directly into the trachea, while the 

 posterior become continuous with those of the contractor tracheae. 



Action. — This muscle retracts the posterior extremity of the trachea within the thorax. 



Relations. — The sterno-trachealis arises close to the origin of the triangularis sterni. 



Nerve supply (?) 



Variations. — -The point at which the sterno-tracheal muscle applies itself to the side 

 of the trachea varies in difi"erent species. In Eudyptes chrysocome from the Falklands, 

 it reaches the trachea 1^ inches, in Eudyptes chrysocome from Kerguelen 1 inch, in 

 Eudyptes chrysolophus 1^ inches, in Spheniscus magellaniciis 2 inches, in Spheniscus 

 demersus If inches, in Spheniscus mendiculus 1\ inches, in Spheniscus minor f of 

 an inch, in Pygosceles tceniatus If inches, and in Aptenodytes longirostris If inches in 

 front of the point of bifurcation of that tube. 



Remarks. — By Cuvier, Tiedemann, and Meckel, the sterno-tracheal muscle is 



