HEART OF REPTILES. 



511 



540 



not only by the ordinary valve on its left side, which is attached 

 to the base of the auricular septum, but by a similar though 

 smaller fold on the opposite or right side : this fold becomes the 

 fleshy auriculo-ventricular valve in birds. To the junction of the 

 two valves at their lower angle a fleshy column is attached. The 

 ventricular cavity, ib. R, which receives the venous blood, propels 

 it to the left aorta, a, and to the pulmonary artery, p : the origin 

 of each is guarded by a pair of semilunar valves. Immediately 

 above the larger of those of the left aorta is an orifice leading 

 into the right aorta: in fig. 339, a bristle is passed from 

 the left aorta through this 

 orifice into the right axil- 

 lary branch, a, of the right 

 or brachio-cephalic aorta. 

 In the figure, the valve is 

 drawn down to show the 

 orifice ; in its natural state, 

 it conceals and would cover 

 the orifice as the blood 

 flowed from the ventricle 

 into the left aorta. Some 

 openings lead from the pul- 

 monic cavity of the ventri- 

 cle into a spongy structure, 

 which has been defined as 

 a particular cavity (spatium 

 interventriculare) of the 

 ventricle ; but it is essenti- 

 ally a part of the pulmonic 

 chamber: bristles are passed 

 through the orifices or in- 

 tercolumnar spaces, leading 

 from R to this structure, in 

 fig. 339. The left auricle, 

 fig. 340, M, when distended, is smaller than the right, and of a more 

 transverse form : its muscular part is produced into an appendage, 

 which almost meets that of the right auricle in front of the ' conus 

 arteriosus,' embracing the ' sulcus coronalis ' of the heart. There 

 is a small pulmonary sinus receiving the short trunks of the 

 pulmonary veins, fig. 340, Z, I. The left auriculo-ventricular 

 aperture is defended by a broad membranous fold continued into 

 the ventricle from the middle of the base of the interauricular 

 septum : to its margin are attached a few chorda? tendinea; : the 



Left auricle and ventricle, Crocodilus dentins 



