ORGANS OF CIRCULATION. 107 



in many, as in the Serpents, Tortoises and Lizards, and also in some 

 Batrachia, sends off one or more tendinous threads upon the apex of 

 the heart. The heart is generally situated far forward and in the 

 middle line. 



As regards the course of the Arteries great differences naturally 

 occur in the several orders and genera, which can not be minutely 

 described in the present work. First of all, a single coronary ar- 

 tery usually arises from the truncus arteriosus. Two carotids are 

 generally present in the Squamigerous Reptiles, but only the left in 

 the Ophidia conveys the blood to the brain ; the right carotid situa- 

 ted more deeply gives twigs to the cervical muscles and ribs. A 

 common trunk usually proceeds from the aorta, for the supply of 

 the viscera, as the stomach, liver, spleen, intestines, and of the mes- 

 entery, or as in the Ophidia, the mesenteric artery arises separately, 

 or many small branches occupy the place of the two. In the Ba- 

 trachia there is found upon the carotid of either side a small dilata- 

 tion, which is formed by the artery here dividing into a number of 

 exceedingly fine vessels, which constitute a spherical spongy kind 

 of vascular rete, through the meshes of which the main trunk of the 

 carotid is continued. In the Serpents several arteries anastomose 

 with the pulmonary arteries, for instance, the hepatic, gastric, and 

 O3sophageal. 



The Veins of the body in which, among the larger Sauria and 

 Chelonia, valves may be demonstrated, usually unite into a posterior 

 and two anterior venae cavae, which pour the blood into the venus 

 sinus already described. 



Reptiles possess a double Portal system, one for the liver, and one 

 for the kidneys, and both of these exhibit somewhat different rela- 

 tions in the several orders. In the Frog the veins of the intestinal 

 canal, of the spleen, &c., concur to form the vena porta of the liver ; 

 those of the abdominal coverings, the urinary bladder, and partly 

 of the posterior extremities, form the portal vessel of the kidneys, 

 while the efferent veins from the latter organs constitute the trunk 

 of the posterior vena cava, into which the blood returning from the 

 sexual organs and liver is poured ; some of the veins of the abdominal 

 parietes empty themselves into the umbilical vein. For a further 

 description of the renal veins the reader is referred to the description 

 of the urinary organs. 



The Lymphatic vessels are highly developed as a system in 

 Reptiles, and form very numerous plexuses, but no glands. The 

 lacteal vessels, which are very abundant upon the mesentery, are 



