348 MESSRS. F. E. BEDDARD AND P. CHALMERS MITCHELL [May 7, 



be obvious (see fig. 2). As will be seen by an inspection o£ the 

 accompanying drawing (fig. 3), which we are enabled to I'eproduce 

 here by the coui-tesy of Prof. Lankester, this half of the valve is 

 bound down anteriorly to the outer wall of the ventricle by a strong 

 muscular bridge. This muscular bridge is also connected with the 

 anterior edge of another valve which is much shorter than the one 

 just described, but which runs a])proximately in the same direction 

 as the last, i. e. nearly parallel to the longitudinal axis of the 

 heart. This has generally been accepted as part of the longer 

 valve and as not corresponding to the septal flap. We are, 

 however, unable to agree with this interpretation of the structure. 

 In its relations it corresponds exactly to the septal flap of the 

 valve of the Alligator ; the upper end of the two valves in the 

 Alligator are in the same way bound down by a strong band of 

 muscle ; it is true that this muscle does not form a definite bridge, 

 but it stands out in relief, and as the spongy wall of the Aeutricle 

 is so much thicker, ^e cannot regard the obliteration of the space 

 beneath as of any morphological significance : in fact we identify 

 what has been called the inner part of the valve in the Bird's heart 

 as the septal flap of the valve of the Alligator's heart. It is 

 identical in relative position, in its mode of attachment ; and in 

 some birds we have seen a slight development of tendon in its 

 substance. Furthermore, the direction of the muscular fibres is 

 not continuous round what has been regarded as the continuous 

 edge of the valve. As to its disproportion in size, we do not see 

 that the amount of development as compared with the nature of 

 the development is a point of much significance. 



The left auriculo-ventricular valve, illustrated in the drawing 

 (fig. 4), consists of two separate vertical flaps, of which the septal 

 is considerably larger and overlaps the left flap ; the septal valve 

 is thinner, and is composed of both muscles and tendon. The left 

 half of the valve has the free crescentic edge strongly ligamentous, 

 the remaining part being muscular. 



The left aorta arises of course from the right ventricle ; its exit 

 is guarded by three watch-pocket valves, on the free edge of which 

 are cartilaginous hardenings ; the exit is narrow, and the aorta 

 then dilates into a wide chamber in the bulbus. In this are two 

 rows of small sculpturings like rudimentary valves extending to 

 the top of the wide part of the aorta, each row- being vertically 

 above the middle of one of the valves (fig. 2, a, b). The pulmonary 

 artery arises from the same ventricle ; its exit is similarly guarded 

 by three valves and it similarly dilates into a wide expansion in the 

 bulbus ; the pulmonary artery at the end of the dilatation di\ades 

 into two branches, which, however, leave the bulbus on its ventral 

 aspect and not, as figured in Wiedersheim, on the dorsal aspect. 



The right aorta arises from the left ventricle ; its narrow exit is 

 guarded by two wide valves, behind the left of which arises the 

 coronary artery. Behind the right lies the very large communi- 

 cation with the left aorta. The aorta then expands into a verj^ 

 wide sac in the bulbus ; in a line with the communication between 



