REPTILES. 217 



aorta, so as to form tlie aorta ahdommalis^ . By tliis union of the 

 arteries from the two sides which meet at the back to form the 

 abdominal aorta, there is formed in the reptiles a vascular ring, in 

 which the oesophagus is situated. 



In many respects the arrangement in the crocodiles is the same 

 as in the other lizards, but there is this modification here in the 

 structure of the heart, that it is divided into two distinct ventri- 

 cles\ In front of the ventricles the different arteries form an elon- 

 gated sac, comparable to the hulhus arteriosus of the fish's heart; 

 this appendage lies with the heart in the pericardium. This arterial 

 sac is formed by the right and left aorta and the pulmonary 

 artery. The left aorta, which here also is* a descending aorta 

 visceralis, arises with the pulmonary artery from the right ven- 

 tricle, and thus conveys venous blood. The right aorta, which 

 divides into an aorta adscendens and a second descending arterial 

 trunk, comes from the left ventricle of the heart. By this arrange- 

 ment the head and the anterior limbs receive arterial ialood, the 

 viscera and the posterior parts of the body mixed blood. At the 

 same time it is not only in the aorta ahdominalis that a mixture 

 of blood takes place, but there is also in the common septum (here 

 cartilaginous) of the two aortic stems an opening concealed behind 

 the semilunar valves, by which, as it seems, blood can pass from the 

 right ventricle into the right aorta, when the animal is under 

 water and the respiration for a time suspended^. The left aorta, 

 arising from the right ventricle, corresponds with that arterial stem 



^ See the figures in an Egyptian Varanus in the elegant dissertation of A. CoETi, 

 J)e systemate vasorum Psamniosauri grisei. VindobonEe, 1847, 4to, fig. i. 



2 The priority of this discovery is due neither to Meckel nor to Martin Saint- 

 Ange, but to Hentz ; Transactions of the A merican Philosophical Society, New Series. 

 Vol. II. Philadelphia, 1825, p. 216 and foil. Comp. my Memoir on the heart of the Cro- 

 codile, Tijdschr. voor. natuurl. Gesch. en Physiol, vi. 1839, ^^- ^S^ — 167. 



3 See BiscHOFF Ueber den Bau des Crocodil-Herzen, in Mueller's Archiv, 1836, 

 g. I — 12, Tab. I. In the beautiful figures, which have been often copied in later 

 works, ex. gr. in the English translation of Mueller's Physiologie, we may remark 

 that G indicates the arteria carotis communis (or according to Rathke the arteria 

 collaris), and by no means the left subclavian artery; E and F are the subclavian 

 arteries. Concerning the origin of the large arteries in crocodiles, which is not always 

 the same but presents varieties of different kinds, we cannot discourse here for want of 

 space. Compare also H. Eathke Ueber die Carotiden der Krokodile und Vogel, 

 Mueller's Archiv, 1850, s, 184 — 192, and further observations by the same, 

 Mveller's Archiv, 1852, s, 374. 



