MULLER] THE AIR-SACS OF THE PIGEON 383 



outgrowth a communicating" canal passes backward to the divertic- 

 ulum suprahumerale. 



The Diverticulum Suprahumerale 



This diverticulum (fig. 12, DSH) is much smaller than the ax- 

 illary one. It covers the head of the humerus, and is bounded by 

 the musculus scapuli humeralis posterior, the musculus triceps cubiti, 

 the musculus biceps brachii, the musculus deltoides major, and the 

 musculus latissimus dorsi. From a small principal cavity, several 

 outgrowths extend between these muscles. It usually communicates, 

 as already mentioned, with the subscapular and axillary diverticula. 

 The connection with the axillary diverticulum is not always de- 

 veloped. 



The Diverticulum Sterxale 



An insignificant diverticulum, hitherto overlooked in the pigeon, 

 arises from the interclavicular sac in the immediate vicinity of the 

 lateral margin of the sternum. This diverticulum (figs. 2 and 11, 

 DST) is attached to the musculus sterno-coracoideus. It is lenticu- 

 lar, and often provided with an outgrowth. 



The Variability of the Interclavicular Sac 



The interclavicular sac and its diverticula are very variable in the 

 pigeon. Some of these variations have been referred to above. In 

 general it may be said concerning them that the development of this 

 system of air-sacs has a relation to the power of flight of the indi- 

 vidual. On comparing these air-sacs in a pigeon that has spent its 

 life in a cage with those found in one that has lived in the open and 

 flown about a good deal, it will be seen that they are much larger and 

 more highly developed in the latter than the former ; it appears that 

 disuse of the wings leads to a reduction of these air-sacs. 



The Sacci Intermedin 



Synonyms 



Bertelli: Sacchi intermedii. 



Campana: Receptacles moyens superieurs et posterieurs. 



Colas: Sac hepatique. 



Fatio: Sacci infracostales superiores et inferiores. 



Gouillot: Receptacles sous-costaux. 



Huxley: Anterior and posterior intermediate air-sacs. 



Jacquemin: Poches souscostales, Cellnles hepatiques. 



Merrem: Erster und zweiter Brustsack. 



Owen : Lateral thoracic cells, Cellulae hepaticse. 



Sappcy: Reservoirs diaphragmatiques anterieurs et posterieurs. 



