410 



COMPARATIVE ANATOMY 



septum ventriculorum is complete or incomplete, is either entirely 

 venous (Crocodiles) or mixed (other Reptiles). Thus even in 

 Crocodiles, although unmixed venous blood passes to the lungs, 

 the systemic arteries contain mixed blood; moreover, a small 

 aperture of communication (the foramen of Panizza) exists 

 between the two aortic roots at their origin, just distal to the 

 valves (Fig. 314). The valves at the base of the main arterial 



A.c.p 



T.a.d 



__.L O.a.v.s 



d.A 



A o. dors. - 



A. cm 



FIG. 314. DIAGRAM or THE HEART or A CROCODILE. 

 (After A. Greil.) 



Ventral view. 



Ac.c.d and Ac.c.s, right and left collateral artery ; A.c.p, pre vertebral carotid ; 

 A.cce, cceliac ; Ao.d, Ao.s, right and left aortic arches or roots ; Ao.dors, 

 dorsal aorta ; A.s.d and A.s.s, right and left subclavian ; At.d and At.s, 

 right and left atrium ; d.A, so-called dorsal anastomosis of the two aortic 

 arches ', F.P, foramen of Panizza; L.B.d, right ligamentum Botalli ; 

 O.a.v.d and O.a.v.s, right and left atrio-ventricular ostium ; P. A, root of 

 pulmonary artery ; R.p.d and R.p.s, right and left pulmonary artery ; 

 S.ao. aortic septum ; S'.ao.p, aortico-pulmonary septum ; S. V, ventricular 

 septum ; T.a.d and T.a.s, right and left innominate ; T r .cand V.s, right and 

 left ventricle. 



stems have undergone a considerable reduction in Reptiles as 

 compared with lower forms ; there is only a single row at the 

 origin of each aorta and the pulmonary artery. Coronary vessels 

 are well developed. 



