508 ZOOLOGY, 
right lung have been entirely removed. The middle line of 
the neck is occupied by the trachea, which overlies the much 
wider cesophagus, which again rests upon two very large 
cylindrical muscles, the powerful retractors of the head. 
The muscles (#) 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 () in 
front, and the pulmonary vein behind ; the three tubes run 
closely parallel forming the so-called root of the lung. 
Each lung (Zu) 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 (Hf) is 
much broader than in the frog or bird. We shall recur to 
its structure presently. 
Below the trachea lies the much larger cesophagus, a cyl- 
indrical tube with muscular walls. The cesophagus termi- 
nates in the stomach (8), 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 
peritoneum, the portal vein (v), and the retort-like gall- 
bladder (@); 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 
