HEART OF REPTILES. 



507 



333 



The pulmonic auricle augments in size with the more exclusive 

 share taken by the lungs in respiration : but the auricular part 

 of the heart shows hardly any outward sign of its division in 

 Batrachians. It is small, smooth, and 

 situated to the left and in advance 

 of the ventricle, in Newts and Sala- 

 manders, fig. 333, a. In Frogs and 

 Toads the auricle is applied to the base 

 of the ventricle, and to the back and 

 side of the aorta and its bulb. The 

 ventricle, usually of a more rounded 

 form than in fig. 331, H, is occupied 

 by the muscular fasciculi, except at a 

 small part between the auriculo-ven- 

 tricular and aortal orifices. The bulbus 

 arteriosus is incompletely divided by 

 opposite longitudinal folds,the margins 

 of which meet, but remain free. 



In Serpents the heart agrees with 



Other Organs in itS elongate form. The Heart, vascular arches, and hyo-branchial 



auricles are in advance of the ventricle, apparatus ' Salamailder 



their lower obtuse ends slightly overlapping its base : they are sepa- 

 rated anteriorly by the co-elongate intrapericardial origins of the 

 arteries called f conus arteriosus,' answering to the bulbous part in 

 Batrachia ; a slight ( auricular ' production of the right auricle is 

 tied down to the arteries by the serous layer of the pericardium. 



The right auricle consists of a sinus and auricle proper. The 

 sinus receives three veins at its fore part ; the orifice of the right 

 jugular and of the inferior azygos is guarded by a pair of valves : 

 in the orifice of the superior azygos I found three semilunar 

 valves ; two veins open at the back or hind part of the sinus, the 

 largest being the postcaval, the smaller one the left precaval. 

 The aperture of communication with the auricle is longitudinal, 

 near the middle of the sinus, of a full elliptical shape, guarded by 

 a pair of membranous valves, situated within the proper auricle. 

 The sinus has the structure of the large veins, with the serous 

 layer of the pericardium reflected over it. The auricle has a 

 finely fasciculate muscular wall, thickest at its lower and fore 

 part. The auriculo-ventricular aperture is a semilunar slit, 

 opening into the base of the ventricle, near the origin of the 

 pulmonary artery, and defended by a short membranous valve, 

 having one or two chordas tendinea3 attached to its free margin. 

 The left auricle is shorter than the right, but of equal breadth 



