Recent Ornitholuyical Publications. 119 



Rodents, Pterodactyles, and many other natural groups of air- 

 breathing Vertebrates ; and it now is manifest that, at the period 

 of the deposition of the lithographic slate, a like variety ob- 

 tained in the feathered class. Its unexpected and almost 

 startling character is due to the constancy with which all birds 

 of the neozoic and modern periods present the short bony tail, 

 accompanied in most of them with that further departure from 

 type exemplified by the coalescence and special modification of 

 the terminal vertebrae, to form the peculiar ' ploughshare-bone ' 

 supporting the coccygeal glands, and giving attachment to the 

 limited number of fanwise radiating rectrices, constituting the 

 outward and visible tail in existing birds. All birds, however, 

 in their embryonic state exhibit the caudal vertebrae distinct, 

 and, in part of the series, gradually decreasing in size to the 

 pointed terminal one. 



" In the embryo Rook the proper extent of the caudal 

 vertebrae is shown by the divergence of the parts of the ilia 

 to form the acetabula; and as many as ten free but short 

 vertebrae are indicated beyond this part. Five or six of the 

 anterior of these subsequently coalesce with each other and 

 with the hinder halves of the ilia, lengthening out the sacrum 

 to that extent. The tail is further shortened by the welding 

 together of three terminal vertebra3 to form the ploughshare- 

 bone. 



" In the young Ostrich from eighteen to twenty such verte- 

 brae may be counted, freely exposed, between the parts of the iliac 

 bones behind the acetabula ; of which vertebrae seven or eight 

 are afterwards annexed to the enormously prolonged sacrum, by 

 coalescing with the backwardly produced ilia; while two or 

 three vertebrae are welded together to form the terminal slender 

 styliform bone of the tail, without undergoing the ' plough- 

 share ' modification. In Archeopteryx the embryonal separa- 

 tion persists with such a continued growth of the individual 

 vertebrae as is commonly seen in tailed Vertebrates, whether 

 reptilian or mammalian. 



" Thus," concludes Prof. Owen, " we discern, in the main 

 differential character of the by -fossil -remains -oldest -known 

 feathered Vertebrate, a retention of a structure embryonal and 



