218 CLASS XV. 



of the mammalian foetus which gives branches to the lungs, but is 

 principally continued into the descending arch of the aor-ta (as the 

 so-named ductus Botcdli). The heart of reptiles, that even of the 

 crocodiles not excepted, is a persistent foetal heart. 



There are one posterior and two anterior venre cavas in reptiles; 

 the posterior cava is formed by the venous trunk of the sexual 

 organs, the hepatic and renal veins. The venous blood of the pos- 

 terior parts of tlie body passes for the most part through the kid- 

 neys before it returns to the hearth 



The lungs of reptiles are larger or smaller sacs with projecting 

 folds on the walls, whence cells arise, which are sometimes very 

 large, and at the lowest part are often entirely deficient. Even when 

 the lungs are large and, as occurs in many, extend far into the abdo- 

 men, the surface presented to the inspired air is rendered by this 

 less composite arrangement relatively smaller than in mammals. 

 When the respiration is interrupted, reptiles do not so quickly die 

 as warm-blooded animals, and they live longer in gases which are 

 unfit for respiration. In many serpents, many species of the genus 

 Coluber, in Vipera berus, there is only one lung present ; Naja, 

 on the other hand, Crotalus, Boa, Anvphisbmna, have two lungs, 

 which in Boa are almost of equal size, whilst in others they are un- 

 equal, so that sometimes there scarcely remains a vestige of one 

 of them, which is mostly the left lung. In the tortoises the lungs 

 are broad and flat ; they extend along the back to the pelvis. The 

 reptiles have no bronchial artery, but the pulmonary vessels appear 

 to supply nutrition to the lungs. The pulmonary veins always 

 terminate in the left auricle, mostly separately, but sometimes after 

 having united to form a single stem'^ In the serpents the anterior 

 part alone of the lungs receives blood from the pulmonary artery; 

 the part that lies farther back receives blood from the abdominal 

 aorta; these arteries anastomose with branches of the pulmonary 



^ Comp. p. 12T. See Gkubt Recherches anatomiques sur le systeme veineux des 

 Grenoidlles, Ann. des Sc. nat. ie Serie, xvii. 1842, Zool. pp. 209 — 230. The vein which 

 Gkuby regarded as running from the anterior abdominal vein to the heart was after- 

 wards shewn by RuscONi to be a cardiac vein that perforates the pericardium and falls 

 into that abdominal vein. Ann, des Sc. nat. 30 S^rie, IV. Zool. p. 282. 



^ Compare on the respiration of reptiles CuVlER Le^. d'Anat. comp. IV. pp. 323 — 

 .326, 330 — 332, 346, 347 (second edition of Ddveenot, vii. 1840, pp. 26 — 40, 86 — 

 100, 128 — 146, 151 — 154), and Meckel Ueber das Respirations- system der ReptUien, 

 Archiv fur die Physiol, iv. s. 60 — 89, Tab. 11. 



