212 



THE FROG— THE PLATANA 



3. The pulmo- cutaneous arch gives off : 



(a) A pulmonary artery along the outer side of the whole length of the lung. 



(b) A cutaneous artery, which at first goes forward to the base of the arm, and 



then spreads out on the skin of the hack of the head.] 



Make a complete sketch of the arterial system. 



Remove the heart, taking care to leave attached to it as much as possible of 

 the large vessels. 



Note the sinus venosus, the conus, the ventral aorta or " truncus arteriosus," 

 the two auricles, and the ventricle. 



Slit open the conus, and notice the longitudinal spiral septum (spiral valve). 

 The openings of the conus are guarded by pocket-valves, three at each end. 



Remove the ventral wall of the two auricles and the ventricle, taking care 

 not to cut away the conus which lies obhquely, across the right auricle. Having 

 washed the blood out of the heart, observe the septum between the right and 

 left auricles, the thick muscular walls and spongy cavity of the ventricle, also 

 the wide auriculo-ventricular opening which is guarded by four valves. In 

 the dorsal wall of the right auricle, near the septum, is the slit-like opening 

 of the sinus venosus with two valves. Near this sinu-auricular aperture, 

 but on the other side of the septum, in the dorsal wall of the left auricle, is 

 the opening of the pulmonary vein from the lungs. 



Respiratory System and Alimentary System (continued). 



1. Remove the mylo-hyoid muscles to expose the hyoid apparatus. Pass a 

 seeker through the glottis to one of the lungs, and slit it open with a pair of 

 scissors. Examine the structure of the lung. 



Duoden"m' <•■" '>'"''''« 



Pyloric conslrictioi 



Cloacal BPerturs 



A B 



Fig. 73. — A. The Alimentary Canal of Bana ; and B. of Xenopri^. 



