PHYLUM CHORDATA 



359 



J, Ao 



Jl.Ao 



Fig. 1002. -Diagram of heart of Turtle. 

 a, incomplete ventriealar septum ; C. p. 

 cavum pulmonale ; Cv. cavum vcnosuni ; 

 L, A. left auricle ; X. Ao, left aortic 

 arch ; P. A. pulmonary artery ; R, A. 

 right auricle ; R. Ao, right aortic 

 arch ; s, arrow showing the course of 

 blood in left aorta ; <, in right aorta ; 

 V. v', auriculo-ventricular valves ; w, 

 arrow showing the course of blood in left 

 auriculo-ventricular aperture ; Xy in 

 right ; y, between cavum venosum and 

 cavum pulmonale ; z, in pulmonary 

 artery. (After Huxley.) 



the heart of the Reptile and that of the Amphibian is that in the 

 former the ventricle is always more or less completely divided into 

 right and left portions. In all the 

 Lacertilia, Ophidia and Chelonia 

 (Fig. 1002) the structure is essen- 

 tially what has been described in 

 Lacerta, the ventricular septum 

 being well-developed, but not com- 

 pletely closing off the left-hand 

 portion of the cavity of the ven- 

 tricle from the right (cavum pul- 

 monale). The left-hand portion, 

 which is much the larger, is further 

 imperfectly divided into two parts 

 — the cavum arterios%tm on the 

 left and the cavum venosum on the 

 right — by the two elongated flaps 

 of the auriculo-ventricular valve, 

 which project freely into the cavity 

 of the ventricle. From the cavum pulmonale arises the pulmonary 

 artery, and from the cavum venosum, the right and left aortic arches. 

 When the auricles contract the cavum venosum becomes filled 

 with venous blood from the right auricle, the cavum arteriosum with 



arterial blood from 

 the left auricle ; the 

 cavum pulmonale be- 

 comes filled with 

 venous blood which 

 flows into it past the 

 edges of the incom- 

 plete septum. When 

 the ventricle contracts, 

 its walls come in con- 

 tact with the edge of 

 the septum, and the 

 cavum pulmonale is 

 thus cut, off from the 

 rest of the ventricle. 

 The further contrac- 

 tion consequently re- 

 sults in the venous 

 blood of the cavum 

 pulmonale being 

 driven out through 

 the pulmonary artery 

 to the lungs, while the blood which remains in the ventricle 

 (arterial and mixed) is compelled to pass out through the 



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cuirt 



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Laicr 



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Fig. 1003.— Heart of Crocodile with the principal arteries 

 (diagrammatic). The arrows show the direction of the 

 arterial and venous ^currents, l.aort. left aortic arch; 

 I. aur. left auricle ; I. am: vent. ap. left auriculo-ventri- 

 cular aperture ; l. ear. left carotid ; I. sub. left subclavian ; 

 /. vent, left ventricle ; puf, art. pulmonary artery ; r. aort. 

 right aortic arch; r, aur. right auricle; r. aur. vent. a-p. 

 right auriculo-ventricular aperture ; r. car. right carotid ; 

 r.suh. sight subclavian; r.vent, right ventricle. (From 

 Hertwig's Lehrbuch.) 



