112 CARNEGIE INSTITUTION OF WASHINGTON. 



To establish stages of development and the probable age of the em- 

 bryos of each stage is one of the difficulties encountered in the study of 

 abnormal development. In an attempt to do this it is necessary to 

 consider the development of the corpus luteum, and much material 

 towards this study has been secured. Incidentally a specimen of true 

 ovarian pregnancy was found located within the cavity of the corpus 

 luteum. This is described in a publication by Franklin P. Mall and 

 Ernest K. Cullen. 



The work of Warren H. Lewis and that of Herbert M. Evans, on the 

 anatomy of embryos, mentioned in Year Book No. 12, has been con- 

 tinued during the past year, and it is planned to prepare them for pub- 

 lication during the coming year. That of Professor Lewis includes the 

 development of the skull and muscles of the head in embryos up to 

 25 millimeters long, whereas that of Professor Evans considers mainly 

 the anatomy of embryos between 2 and 4 millimeters long, together with 

 the surface anatomy of older stages. The work of George W. Corner 

 on the development of the pancreatic duct and the structural unit and 

 growth of the pancreas has been published during the past winter. 



The observation of Eleanor Linton Clark and Eliot R. Clark on the 

 movements of the lymph heart in the living chick embryos are of inter- 

 est in connection with the discovery that the muscle of the lymph 

 heart is derived from the myotomes. They observed that the early 

 movements of the lymph hearts are always associated with movements 

 of the body and tail and that the lymph-heart beat is gradually dis- 

 sociated from other movements. 



A study of the development of the azygos veins has been carried 

 on by Professor Sabin, who finds that the azygos veins are not remnants 

 of the posterior cardinal vein, as has hitherto been thought, but that 

 they are entirely new veins that develop for the drainage of the pre- 

 vertebral tissues, and their increase in size is a consequence of their 

 taking over the intercostal veins. This study opens up the larger 

 problem of the relation of the great veins of the adult to the primitive 

 veins of the embryo, and indicates that it is the vena cava that replaces 

 the posterior cardinal vein and not the azygos veins. Only a prelim- 

 inary report of this study has been published. 



The study of Lewis H. Weed on the medulla, by means of reconstruc- 

 tion, has been brought to a conclusion, a summary having been pub- 

 lished in the Anatomical Record, the completed paper appearing as 

 Publication No. 191 of the Carnegie Institution of Washington. In 

 this work an attempt has been made to secure a more detailed account 

 of the gray matter of the human medulla, partly in order to assist in 

 following its development. This latter work has been carried on by 

 Professor George L. Streeter and Dr. Charles R. Essick for a number of 

 years and Dr. Weed's contribution will be of especial value to them. 



