78 
HEPBURN, Davin, 1894—95, Abnormal kidneys from domestic pig. Journ. of 
Anat. and Phys., vol. 29. 
Hits, H. E., 1899, Philadelphia Med. Journ. 
JEIDELL, Hetmina, 1911, A note on the source and character of the early 
blood vessels of the kidney. The Anat. Record, vol. 5. 
Mc Moraics, J. P., 1898, A case of congenital dystopy of the kidney with 
fusion. Journ. of Anat. and Phys., vol. 32. 
MuTananN, E., 1907, Die Hufeisenniere. Anat. Hefte, Bd. 32. 
Naumann, A. H., 1897, Über die Häufigkeit der Bildungsanomalien der Nieren 
Dissertation, Kiel. 
Poutmann, A. G., 1905, Abnormalities in the form of the kidney and ureter 
dependent on the development of the renal bud. Johns Hopkins 
Hospital Bull. 
ScHOENLANK, W., 1913, Dystopia renis Sagittalis et Transversa. Morph. Jahrb., 
Bd. 45. 
SCHUHMACHER, E. von 1903, Ein Fall von gekreuzter Dystopie der Nieren. 
Wiener klinische Wochenschrift, Bd. 16. 
SCHWALBE, E., 1904, Ein Fall von seltener Nierenmißbildung. Münchener medi- 
zinische Wochenschrift, Bd. 151. 
Sımon, Cu., 1897, Un cas de “rein en fer a cheval.” Bibliogr. Anat. 
STRUBE, G., 1894, Uber congenitale Lage- und Bildungsanomalien der Niere. 
Arch. f. pathalog. Anat. u. Phys., Bd. 187. 
Tweepy, H. C., 1893, A case of single unilateral kidney. Journ. of Anat. and 
Phys., vol. 28. 
Nachdruck verboten. 
On Stages in the Development of Human Embryos 
From 2 to 25 mm. Long. 
By Franxuin P. Matt, 
Professor of Anatomy, Johns Hopkins University, Baltimore, Maryland. 
It is customary among physicians to classify embryos and fetuses 
according to their age and this is quite natural for the most common 
question asked about a specimen is the one regarding its age. Ana- 
tomists have attempted to answer the question of age, first by ex- 
pressing an opinion regarding it, and later by examining critically 
all available data bearing upon it. To the first category of anatomists 
belong SÖMMERING, E. H. WEBER, ARNOLD, Ecker, KOELLIKER and ToLDT, 
and to tho second, von BAER, REICHERT and His. 
It is quite apparent why it should be difficult to determine in 
a satisfactory way the age of human embryos; the time of fertilization 
