246 ON THE ANATOMY OP THE CONDOR. [Apr. 1 5, 



far from the end of the complete half of the valve. The seam, as 

 I call it, has hardly a muscular or tendinous appearance. It is 

 not perceptibly raised above the muscle which forms the wall of 

 the heart ; it is only conspicuous through its decided white 

 colour. This description, I should observe, applies to the heart 

 after preservation in spirit. I received the whole bird from 

 Australia in spirit some years since. But the seam is so marked, 

 that I cannot but think that it would have been as obvious in 

 the fresh heart as it is in that preserved in spirit. The appear- 

 ance of the seam, in fact, suggests a thickening of the lining- 

 membrane of the heart, the endocardium. It just runs on to 

 the commencement of the left-hand piece of the muscular existing 

 valve. Now it appears to me to be fair to construe this structure 

 as a remnant of the otherwise chiefly missing septal flap of the 

 atrio-ventricular valve. It may be admitted that its course is 

 straighter than such a flap had when fully developed. But with 

 rudimentary structures, alterations of one kind or another not 

 related to their former functions are not uncommon. I do not, in 

 fact, think that the length of the seam is against my interpreta- 

 tion of its nature. As to the possibility that it is a thickening of 

 the endocardium, it seems to me that it is then very comparable 

 to the "fold" described by Gegenbaur, "which is formed by a 

 thickening of the endocardium." And Gegenbaur adds to the 

 description that the fold in question arises " from the anterior 

 origin of the muscular valve on the septum ventriculorum," which 

 is precisely the origin that the seam described here by myself has. 

 Gegenbaur's fold, however, runs " obliquely backwards and down- 

 wards," so that its position as a rudiment is more in accord with 

 that interpretation. A final point is of some little interest. It 

 is or has been believed that ontogenetically as well as phylo- 

 genetically the muscular or tendinous valves of higher vertebrates 

 are first formed as simple thickenings of the endocardium, later 

 invaded by muscle which itself later on is converted into tendon 

 (as in higher mammals). The return, so to speak, of this rudi- 

 ment of the septal half of the valve to its very earliest condition 

 is worth emphasizing. 



The facts that have just been dealt with raise another inter- 

 esting question. At one time the descent of Birds from some 

 Dinosaurian form was widely believed in ; later this view lost 

 some ground, until quite recently Prof. Osborn has recommended 

 its serious reconsideration mainly on the grounds of the discovery 

 of a fourth toe bent backwards, which has been shown to exist in 

 the Dinosauria. This and some other features have added not a 

 little to the bird-like characteristics of that gi-oup of Reptiles. 

 On the other hand, there have not been wanting those who would 

 assign the origin of Birds to a lower type of Reptile. The nature 

 of the heart-valves seems to me to throw some light upon the 

 question. At first sight, the arrangement of the auriculo- 

 ventricular valves in the bird is more suggestive of the same 

 valves in the tortoise than in the crocodile, the latter repre- 



