EEPORT ON THE SPHENISCIDiE. 215 



The Air Sacs. 



The air sacs in every species of Penguin which I have examined are nine in number. 

 Of these four pairs are placed symmetrically on either side of the middle line, while the 

 ninth is single and occupies the middle line of the body. The first four pairs, from their 

 relations to neighbouring organs, may be named the hepatic, the pericardiac, the 

 abdominal, and the cervical, while the ninth or azygos air cell may be termed the inter- 

 clavicular. 



The following description is drawn up from a special dissection of Eudyptes chrysocome, 

 but apart from dimensions, is equally applicable to the other species examined : — 



The first, or hepatic air sac, extends from the axiUa, where it is bounded in front by 

 the subclavian artery, backwards as far as midway between the last rib and the anus. 

 On the outer side it is in contact with the ribs and intercostal muscles, while on the 

 inner side it is bounded from before backwards by the heart and pericardium, by the 

 outer side of the liver, and by the transversalis abdominis muscle. The wall of this sac 

 is attached to the whole length of the thoracic surface of the sternum internal to the 

 sternal notch. The sac itself is divided incompletely into two parts by means of a trans- 

 versely-disposed septum. This septum is situated opposite the posterior border of the 

 lung. The hepatic air sac derives its air directly from the lung, by means of an aperture 

 which is situated on the inner surface of the lung, close to the inferior border of that 

 organ behind the septum above described. The posterior extremity of this sac intervenes 

 betvreen the obliquus externus and transversalis abdominis muscles. 



The second, or pericardiac sac, lies below the pericardium. It is bounded below by 

 the anterior half of the thoracic surface of the sternum, and above by the heart and 

 pericardium, while on the inner side it is in contact with its fellow of the opposite side. 

 It does not communicate directly with the lung, but receives its air through the 

 intervention of the hepatic sac, by means of an aperture which, in Aptenodytes, is 

 of sufticient size to admit of the passage of two fingers.^ This aperture of com- 

 munication is situated directly above the external or costal process of the sternum. Thus 

 the pericardiac sac only communicates indirectly with the bronchial tubes. 



The third and largest of the air sacs is the abdominal. It extends from the posterior 



^ According to Milne- Edwards (Legons sur Pliysiologie et TAnatonue Conipar(5e, vol. ii. p. 353,) the pericardiac air sac 

 (le rdservoir diaphragmatique ant^rieur of that author) receives its air directly from the lung in the majority of birds. 

 Such, so far as I could ascertain, is not the case in any species of Penguin. At the same time it is right to observe that 

 in the majority of the birds dissected the means used in preserving the specimens occasioned considerable difficulty in the 

 recognition of the various apertures of communication between the lungs and the air sacs. The existence of five distinct 

 apertures in the lung of most of the species examined certainly leads to the conclusion that in the Penguins, as in other 

 birds, each of the air sacs communicates with the lung by means of a separate aperture. 



In the work quoted will be found a very complete list of authors who hav6 directed theii' attention to the respiratory 

 organs of birds. That list I do not think it necessary to repeat here. 



