XIII 



PHYLUM CHORDATA 



269 



coil. The large intestine or rectum (ret.) is very wide and short, 

 and passes without change of diameter into the cloaca (cl.). 



The liver (Ir.) is two-lobed ; between the right and left lobes 

 lies a large gall-bladder (Fig. 941, G). The pancreas (P.) is an 

 irregular gland sur- 

 rounding the bile- 

 duct, into which it 

 pours its secretion ; 

 the spleen (Fig. 940, 

 spL) is a small, red 

 globular body at- 

 tached near the 73^ 

 anterior end of the 

 rectum. The thyroids 

 are small paired 

 organs lying below 

 the floor of the 

 mouth in front of 

 the glottis. The 

 thymus is also 

 paired, and is 

 situated behind and 

 below the tympanic 

 membrane. 



Respiratory 

 Organs. The 

 lungs (I. Ing., r. Ing.) 

 are elastic sacs lying 

 in the anterior part 

 of the coelome above 

 the heart and liver ; 

 their size and 

 appearance vary 

 greatly according 

 to their state of 

 distension. Each contains a spacious cavity and has its walls 

 raised into a complex network of ridges abundantly supplied 

 with blood-vessels. The two lungs open anteriorly into a small 

 laryngo-tracheal chamber which communicates with the mouth by 

 the narrow slit-like glottis. The walls of the laryngo-tracheal 

 chamber are supported by a cartilaginous framework, and its 

 mucous membrane is raised into a pair of horizontal folds, the 

 vocal chords, by the vibration of which the croak of the Frog is 

 produced. 



In breathing, the Frog keeps its mouth closed, and by depressing 

 the floor of the mouth, draws air into the buccal cavity through 

 the nostrils. The floor of the mouth is then raised, the nostrils, 



FIG. 941. Rana esculenta. Stomach and duodenum with 

 liver and pancreas. Dc., Dc. 1 common 'bile-duct; Dc. 2 its 

 opening into the duodenum ; D. cy. cystic ducts ; Dh., 

 Dh. 1 hepatic ducts ; Du. duodenum ; G. gall-bladder ; 

 L, L 1 , LZ, L' A , lobes of liver, turned forwards ; Lhp. duodeno- 

 hepatic omentum, a sheet of peritoneum connecting the 

 liver with the duodenum ; M, stomach ; P. pancreas ; P 1 , 

 pancreatic duct ; Py. pylorus. (From Wiedersheim's Com- 

 parative Anatomy.) 



