508 ZOOLOGY. 



right lung have been entirely removed. The middle line of 

 the neck is occupied by the trachea, which overlies the much 

 wider oesophagus, which again rests upon two very large 

 cylindrical muscles, the powerful retractors of the head. 

 The muscles (R) extend backwards along the vertebral 

 column, behind the heart and through the abdomen. The 

 trachea branches just in front of the heart, to send a 

 bronchus to each lung. The left bronchus can be seen in 

 the figure, passing between the pulmonary artery (p) in 

 front, and the pulmonary vein behind ; the three tubes run 

 closely parallel forming the so-called root of the lung. 

 Each lung (Lu) is a large elastic sack with numerous air- 

 cells. The size of the lung depends upon its degree of ex- 

 pansion; when entirely collapsed it is quite small, but it may 

 easily be blown up through the trachea. The heart (Hi) is 

 much broader than in the frog or bird. We shall recur to 

 its structure presently. 



Below the trachea lies the much larger oesophagus, a cyl- 

 indrical tube with muscular walls. The oesophagus termi- 

 nates in the stomach (S), which, together with the remaining 

 digestive organs and the spleen, is drawn aside in the figure. 

 The long and coiled intestine can be followed to the point 

 where it passes under the oviducts (ovd) and the bladder 

 (Bl] to terminate in the cloaca, the external opening of 

 which is represented at Cl. The main mass of the elongated, 

 gray, and mottled liver lies upon the intestine, being turned 

 so as to show its raphe (m), by which it is suspended from the 

 peritonaeum, the portal vein (v), and the retort-like gall- 

 bladder (G) ; the gall duct passes through the body of the 

 pancreas (Pan), an elongated whitish mass resting upon the 

 first coil of the intestine, the so-called duodenum. Alongside 

 the pancreas is the much smaller dark oval spleen (Sp). 



The specimen figured is a female killed during the period 

 of reproduction. The genital organs are therefore enor- 

 mously developed. The long and prominent oviducts con- 

 tained eggs already provided with a shell. The right 

 oviduct is seen drawn out and suspended by a mesentery, a 

 thin and transparent membrane with numerous blood ves- 

 sels. The lower end of the oviduct is seen through the 



