244 ZOOTOMY. 



apertures by which they respectively communicate with the lung ; the 

 corresponding aperture of the anterior intermediate is in its antero- 

 internal corner. The apertures of the other air-sacs are much more 

 diffcult to see : that of the sub-bronchial ( 164) lies in its posterior 

 wall just dorsal to the entrance of the bronchus into the lung : the 

 prebronchial extends backwards to the anterior end of the lung and 

 there opens (see 286). 



277. The costo-pulmonary muscles, small fan- 

 shaped sheets of muscle, arising from the junctions of the 

 sternal and vertebral ribs, and passing into an aponeurosis 

 which covers the ventral surface of the lungs, between the 

 dorsal walls of the air-sacs and the pleura. 



278. The pulmonary pleura, a delicate membrane, 

 continuous with the peritoneum and immediately investing 

 the ventral surface of the lungs : to see it the costo- 

 pulmonary muscles and their aponeurosis must be removed. 



XLIV. Cut through the trachea about an inch anterior 

 to its bifurcation : dissect away the lungs from the 

 dorsal body wall and remove them from the body 

 with the bronchi and posterior end of the 

 trachea : note : 



279. The transverse depressions on the dorsal surface of 

 the indistensible lungs, corresponding to the ribs, and the 

 intervening elevations which fit into the intercostal spaces. 



280. The dilatation of the posterior end of the trachea 

 into the syrinx (Fig. 57, sy), or "lower larynx." 



281. The intrinsic syringeal muscles, paired narrow 

 bands arising from the sides of the trachea about an inch in 

 front of its bifurcation, and passing backwards to be inserted 

 into the sides of the syrinx. 



282. The complete tracheal rings, their ventral halves 

 bony, their dorsal halves cartilaginous. 



283. The bronchial half-rings, along the outer side of 

 each bronchus ; the first is bony, the rest are cartilaginous : 



