210 



ANATOMY OF VERTEBRATES. 



membrane, and the pleura is reflected over the sternal surface 

 only, to which the strong aponeurosis of the diaphragmatic muscles 

 is attached. They are consequently smooth and even on that 

 surface, but posteriorly are accurately moulded to the inequalities 

 of the ribs and intercostal spaces : the bosses varying in number 

 from four to seven {Apteryx^ or eight (Emeu). 



The lungs in general are of a bright red colour, and of a loose 

 spongy texture. The bronchi, fig. 85, v, fig. 95, «, penetrate 

 their mesial and anterior surfaces about one-fourth from the upper 

 extremities, become membranous, dilate, give off branches, which 

 diverge as they run along the anterior surface; and the trunk 



divides into the two which open 

 ^^ at 5, Z>, into the thoracic-ab- 



dominal air-receptacles. These 

 orifices are oblique, and are par- 

 tially covered by a slight projec- 

 tion of membrane. Some cartila- 

 ginous traces are found through 

 their entire extent. 



The pulmonary artery divides, 

 almost immediately after its ori- 

 gin, into two branches, one to 

 each lung; the ramifications of 

 each artery form plexuses, fig. 

 96, B, which chiefly compose the 

 pulmonary tissue : the pulmo- 

 nary veins leave each lung by a 

 single trunk, and the two trunks 

 unite into one before terminating 

 in the left auricle. 

 The superficial primary branches 



A. Lobule of the lung of a bird represented in ideal ^f f|,p Kvn-nplii -ficr Q'^ n n QPnrI 

 longitudinal section, cclxviii. ^^ ^'^^ DlOnCUl, Ug. yO, C, C, SCnCl 



off deeper-seated secondary ones, 

 fig. 96, «, «, which maintain a uniform diameter to their c^ecal 

 terminations : the tertiary bronchi, ib. h, h, distributed penniformly, 

 also maintain a regular diameter, and open upon a dense laby- 

 rinth of blood-vessels, ib. B. The mucous ciliated lining of the 

 bronchi ceases with them ; and the capillaries of the pulmonary 

 tissue are covered only by a hyaline epithelium, so as to appear 

 naked. ^ The ultimate pulmonary capillaries do not form a net- 

 work lining definitely bounded air-cells, but each capillary crosses 



' CCLXVIII. p. 277. 



