524 



CHORDATA 



This is iiilcrlarsal. occurring between the first and second rows of tarsal 



bones (i\g. 5S7, C). 



Since reptiles lack evert transitory gills, the gill slits are completely 



degenerate Ijefore the young escapes from the egg. Dermal respiration is 



far less imporLant tlian with the Amphiliia, lungs, as in birds and mammals, 



beiiig the respiratory organs, arid in these 

 a progressi\'e developmeirt mav be fol- 

 lowed. The larvnx is followed bv a 

 trachea with cartilage supports in its 

 wall, and this either opens directly iitto 

 the two luiigs or di\"ides into two bronchi, 

 which, in Wirainis, may di\-ide again 

 inside the lungs. The lungs in the more 

 primiti\e forms are subdivided only per- 

 ipherally, but in the higher groups the 

 whole is chambered, partitions extendiirg 

 inwards to the intrapulmonary bronchus 



(tig. 536)- 



Since the respiration is entirely 

 pulmonary, the heart is divided into a 

 left arterial and a right vertous half, and 

 a correspondiirg separation of systemic 

 and pulmonary blood-vessels occurs (tig. 

 574). The two auricles are completely 

 separated, while a septum extends into 



Fio. 574.— Heart of crocodile with t^g ventricle, complete in the crocodiles, 

 arteries (diagram I. a', j-, riglit and 



left auricles; aJ. as, right a^nd left but not in turtles, lizards, and snakes, 



aortic arches; f,carotidsu>',o-, right Yet even in tire crocodiles a mixing of 

 and left aunculo-\"entricular ostia; 



/-, pulmonarvarterv; i, subclavians; arterial and A'enous blood occurs since 



r',i'=, right' and left ventricles (the ;„ the large aortic trunks which arise 

 arrows show tlie direction of the 



from l)oth ventricles a communication, 



the Jonimcn ranizzir, persists. The 

 arterial trunk is divided by internal 

 partitions into three vessels, wliich are 

 but rarely \isible from the exterior. One 

 of these arises from the right ventricle, 

 carries venous blood, and takes over the fourth arterial arch, which 

 gives off the pulmonary arteries (4, />). A second \-essel arises from the 

 left ventricle, is purely arterial and connects with most of the remaining 

 arterial arches, the first, which gives off the carotid, and the right half 

 (aortic arch, ad) of the second arch. The third vessel connects on the 



blood flow); i, 2, 4, arches compara- 

 ble with those of amphibia. Notice 

 the origin of the ^•essels from the 

 heart, and the connection (foramen 

 Panizza?) between the arterial trunk 

 and the left aortic arch, just in front 

 of the heart. 



