166 DEVELOPMENT AND EEDUCTION OF THE TAIL 



of the spinal cord, and which forms an irregular, evaginated space in the conus 

 meduUaris; (2) an under part, which gradually narrows toward its caudal end and 

 terminates blindly in the filum terminale. 



The various investigations of the occurrence of tails among adults, children, 

 and newborn infants have given rise to a great deal of discussion. Bartels (1884) 

 published an exhaustive study of the occurrence of tails among the human race. 

 Other pubhcations on the subject have appeared from time to time, notably bj^ 

 Virchow (1884), Oskar Schaeffer (1892), Pyatnitski (1892), Dickinson (1894), Berry 

 (1894), Kohlbriigge (1898), Watson (1900), and others. Harrison (1901) describes 

 the histological structure of a large, well-developed tail which was removed from a 

 child six months old. He states: 



"Two weeks after the birth of the child the tail was 4.4 cm. long; at the age of two 

 months it had grown to 5 cm., and at six months, when it was removed, it had attained 

 a length of 7 cm., showing altogether a fairly rapid rate of growth. The most remarkable 

 characteristic of the tail was its movability. * * * Beneath the skin the main bulk of the 

 tail was made up of areolar tissue containing much fat. Blood vessels, nerves, and striated 

 muscle fibers are embedded in this mass. There is no trace of anything like the medullary 

 cord or of notochordal tissue." 



More recently similar observations have been made by Brugsch (1907), Kon- 

 stantiowitsch (1907), and Schwarz (1912). 



MATERIAL AND METHODS. 



The material upon which this study is based consists of 44 specimens in the 

 Carnegie Collection of human embryos, Baltimore. They range from 4 to 125 

 nun. CR length, and a table of them, with their respective measurements, is shown 

 herein. The specimens, for the greater part, had been carefully preserved in 10 

 per cent formahn and dehydrated in alcohol. The smaller ones were embedded in 

 paraffin, the larger ones in celloidin, and most of them were cut in serial sagittal 

 sections varying in thickness from 20 to 200 n in the different specimens. A large 

 proportion of the specimens were stained m toto in alum cochineal and borax car- 

 mine before embedding; others were stained on the slides with hematoxylin and 

 eosin or similar stains. From 15 to 80 sagittal sections through the median part 

 of each embryo were used in this investigation, and usually one graphic recon- 

 struction was made of each specimen, although all of these are not illustrated. 

 They present a median profile view disclosing some structure — for instance, the 

 winding caudal end of the chorda dorsaUs or the sympathetic ganglia. In the 

 illustrations these are slightly schematicized in order to show distinctly their actual 

 relations. The graphic reconstructions were made by copying each section on 

 transparent paper from a projection apparatus. When the drawings under the 

 projection apparatus were completed the sheets were piled so that adjacent sec- 

 tions were accurately fitted one upon another. The desired parts of the sketch 

 on each sheet were then copied on another sheet of paper, due attention being 

 given to the form and relation of the component parts. This procedure was facili- 

 tated by the use of a glass table illuminated from below. In the case of cross- 



