THE RESPIRATORY APPARATUS IN BIRDS. 561 



towards the median plane. In all, they are independent of each other, and 

 freely communicate either with the lung by a single aperture, or with the bones 

 by one or more openings. Lastly, in all they are nine in number. 



" These reservoirs are : the thoracic sac, situated at the anterior part of the 

 thorax ; two cervical reservoirs, situated at the base of the neck ; two anterior 

 diapkrarjmatic reservoirs, placed between the two diaphragms ; two posterior 

 diaphragmatic reservoirs, also between these two diaphragms, but behind the 

 preceding ; and, lastly, tivo abdominal reservoirs, placed against the 6ui)erior wall 

 of the abdomen. Of these nine reservoire, the first only is single and symmetrical ; 

 the othei's are pairs, and similarly arranged on each side of the median plane. 



" The thoracic and cervical reservoire are situated beneath, and in front of, 

 the lungs ; the abdominal reservoire lie behind these organs, and the four 

 diaphragmatic sacs at their inferior part and between the preceding ; hence the 

 denomination of middle reservoirs sometimes applied to the latter, in opposition 

 to the first, which are named the anterior reservoirs, and to the second, called the 

 posterior reservoirs." 



External Conformation of the Reservoirs. — 1. Thoracic reservoir 

 (Fig. 'd'dl, 2}. — '' It is situated above the clavicles and the inter-clavicular space, 

 in the cavity of the thorax, which it extends beyond on each side to the roots of 

 the wings, around the articulation of the shoulder. It is related with : above, 

 the trachea and oesophagus on the middle plane, the lungs and the origin of the 

 cervical reservoirs on the lateral parts ; below, with the sternum, the clavicles, 

 and the interclavicular aponeurosis ; behind, with the heart and anterior 

 diaphragmatic reservoirs, beneath which it is prolonged by forming on each a 

 long point ; in front, with the integuments of the neck, which it raises into 

 a hemisphere in Palmipeds, but which is angularly depressed in other classes ; on 

 the sides, with the sternal ribs, the two clavicles, and the membrane uniting them. 



" The prolongations which arise from the lateral parts of these reservoirs, and 

 cross the walls of the thorax to pass around the articulation of the shoulder, are 

 three in number, and may be distinguished into inferior or subpectoral, superior 

 or subscapular, and middle or humeral. 



" The subpectoral prolongation (Fig. 337, d) issues from the thoracic reservoir 

 by an orifice situated behind the posterior clavicle, and passes beneath the tendon 

 of the great pectoral muscle, where it spreads out as a lenticular cavity. The 

 relations it contracts with that muscle are remarkable : in Birds, still more than 

 in Man and a gi'eat number of quadrupeds, the tendon of the great pectoral is 

 fonned of two parts, one direct, the other reflected ; it is between these two 

 portions that this small air-sac is insinuated, and where it forms a very firm 

 connection with them ; the effect of which is, that at the moment the great 

 pectoral muscle contracts, it dilates the subjacent cell and draws into it a greater 

 quantity of air. 



" The subscapular and humeral prolongation communicate with the principal 

 reservoir by a common opening placed behind the small adductor muscle of the 

 humerus. After leaving this orifice, the subscapular sac spreads under the 

 scapular and sul)scapular muscle, which it separates from the ribs and corresponding 

 intercostal muscles ; it is developed more particularly in a longitudinal direction. 



" The humeral prolongation occupies the axilla ; it is smaller than the 

 preceding, of a pyramidal form, and opens by its summit into an infundibular 

 fossa, which leads to the canal of the humerus. 



" The thoracic reservoir differs from all the others by the extremely numerous 



