March, 1895. THE HABITS OF ARCH&OPTERYX. 181 



perfectly fitted, by their form and arrangement, for the purpose of 

 flight as in, say, a pigeon. Their size, though not difficult to deter- 

 mine absolutely, is difficult, if not impossible to determine relatively 

 to the weight of the body ; for in our guesses at the weight of the 

 animal a very large margin must be left for possible error. 



The rectrices, or tail-quills, differ very remarkably from those of 

 any other known bird. Unfortunately, I overlooked the question as 

 to their number when I was in Berlin. Previous authorities regard 

 them as arranged in pairs, one pair to each vertebra of the tail, but 

 Dames is very cautious on this point. My large photographs suggest 

 that they are somewhat more numerous, but the point is one which 

 may be left for the present undetermined. They differ from the 

 corresponding feathers of modern birds of flight chiefly in size, being 

 very much smaller than those of ordinary birds of equal size. Those 

 of the anterior part of the tail are about 50 mm. long, or perhaps a 

 little less (Berlin specimen). Further back they are longer, the 

 maximum length of about 95 mm. being at about the twelfth caudal 

 vertebra. To what extent, if any, they could be spread out and 

 closed together we can only guess, and the fact that they lie in both 

 specimens at an angle of about 30 to the axis of the tail does not 

 help us much ; for, if the animal had the power of spreading its tail- 

 feathers, this would perhaps have been effected by means of a muscle 

 arising from some bone in the pelvic region, through the mediation of 

 a slender tendinous band running along each side of the vertebral 

 column of the tail, and opposed by a slender elastic ligament which 

 would, when the muscle was relaxed, bring the feathers into some 

 such position as that which they occupy in the fossils known to us. 

 These tendons and ligaments may well have been very small, and the 

 absence of any trace of them in the fossils is not sufficient justification 

 for our stating that they did not exist. We must, therefore, remain 

 in ignorance as to whether Avchaoptevyx could or could not spread and 

 close its tail. 



Though the feathers are small, their great number gives to the 

 tail, looked upon as an aeroplane, a very considerable surface, and 

 this surface is greatly increased by the development of a series of 

 feathers, which may perhaps be classed as rectrices, along the sides 

 of the hinder part of the trunk. So far as I can make out by means 

 of drawings that I have made to scale of the bird in the flying 

 position, these lateral rows of feathers constitute with the tail-feathers 

 a continuous aeroplane, extending forwards as far as the posterior 

 edge of the extended wings. Why those who have made drawings 

 of the animal "restored" should all, so far as I know, ignore the 

 existence of this lateral aeroplane, and represent the lateral feathers 

 of the tail-series as coming to an end in the tail, is a subject which 

 those who are interested in the origin and multiplication of errors 

 may appropriately consider ; but this is not the place for the con- 

 sideration of it. ft is sufficient here to point out that the extant 



