Characteristics of the Vertebrata. lix 



left aorta, before the posterior part of the ventricular cavity, into 

 which the blood from the left auricle is discharged, commences to 

 contract. When this part of the ventricular mass beg-ins to con- 

 tract upon its arterialized contents, access to the pulmonary artery 

 has been cut off by the closing- up of the muscular demi-canal 

 leading" to that outlet ; and the arterialized blood is consequently 

 thrown into the two systemic aortae. Of these, the one which 

 bends over the left bronchus, or, in Opludia, to the left side of the 

 body, and which is consequently known ordinarily as the left aorta, 

 never gives any branches to the anterior j)arts of the body ; but 

 either as in Sauria and Ophidia^ simply joins the right aorta without 

 giving off any branches; or, as in Loricata, distributes itself to 

 the chylo-poietic viscera, and communicates with the right aorta 

 simply by a branch of anastomosis. In the Crocodilina this vessel 

 arises from the right auricle, together with the pulmonary artery, 

 and consequently never carries any arterialized blood. Its com- 

 munication, by the foramen Panizzae, with the right aorta, which 

 supplies the anterior parts of the body, may be held to foreshadow 

 the conversion which the fourth left aortic arch undergoes into a 

 left subclavian artery in Aves. The close j)roximity of the com- 

 mencement of the left aorta to that of the pulmonary artery, enables 

 it in all Reptiles alike to relieve the pulmonary circulation, when 

 respiration may be put into temporary abeyance. The arterial 

 outlets of Reptiles have only two semilunar- valves. In all Reptiles, 

 as in all Birds, there are two superior as well as one inferior vena 

 cava ; but in Reptiles these three vessels open into a pulsatile 

 venous sinus, and have their contents poured through it by an 

 orifice guarded with eyelid-like valves into the ventricular cavity. 

 In all Reptiles there is a ^ renal portal ' circulation, by which the 

 venous blood returning from parts placed posteriorly to the kidneys 

 finds its way into these organs, at the same time that by means of 

 anastomoses with factors of the true portal system, it may be 

 returned to the heart by way of the hepatic system. The supra- 

 renal bodies are,' like the renal, possessed of a system of venous 

 inferent vessels. The lymphatic vessels, which often take the shape 

 of loose sheaths surrounding the large arteries, communicate with 

 the veins both anteriorly in the brachiocephalic, and posteriorly in 

 the caudal regions. Upon their junction with the veins of this 

 latter region, contractile sacs, the so-called ' lymphatic hearts,^ are 



