DEPARTMENT OF EMBRYOLOGY. 77 



clearly shown how this is followed by a third phase, in which the primary 

 pattern becomes gradually modified and adapted to the developing structures 

 of the limb until the adult arterial pattern is attained. The arm-bud is not a 

 favorable place to study the first phase, or origin of the endothelium, because 

 of the dense character of the mesenchymal core. The nuclei of the mesen- 

 chyme cells are so closely packed that one can not satisfactorily observe the 

 differentiation of the first angioblasts or the manner of their transition into 

 capillaries. In Dr. Woollard's youngest stages there is a definite capillary 

 net connecting by dehcate feeders with all of the adjacent segmental arteries, 

 and this, it may be mentioned, is the only trace of segmental character shown 

 by the vessels of the arm. That the seventh segmental becomes the domi- 

 nating feeder to the arm is attributed by him to the accident of its lying 

 opposite the center of the growing limb-mass, and so receiving the maximum 

 stimulus or phj^siological pull on the part of the capillary net. 



NERVOUS SYSTEM AND ITS MEMBRANES. 

 Earliest Landmarks in the Human Embryo Brain. 

 For several years past Professor G. W. Bartelmez, in conjunction with 

 Professor H. M. Evans, has been studying the external form and finer anatomy 

 of the human embryo during the third week of development. Owing to the 

 scarcity of normal and well-preserved specimens of this period, progress has 

 been difficult and slow. Through the cooperation of several other laboratories, 

 both in this country and abroad, it has been possible to complete a careful 

 study of 14 embryos, ranging from 2 to 16 somites, and this has resulted in a 

 large amount of important data and observations which are now being put in 

 form for publication. Shorter communications have already appeared, and 

 during the past year Dr. Bartelmez has pubhshed an account of the neural 

 folds as they occur in these specimens. He has given us for the first time 

 landmarks by which it is possible to trace the primary subdivisions of the 

 brain from the time of the appearance of the somites. Being able to map out 

 accurately those portions of the medullary folds that enter into the formation 

 of the forebrain, midbrain, and hindbrain, respectively, as Dr. Bartelmez has 

 made it possible to do, is, of course, of fundamental importance both to the 

 embryologist and the comparative anatomist. The earliest landmark to 

 make its appearance is a marked enlargement of the neural folds in the region 

 of the otic plate. This constitutes the otic segment and is characterized both 

 by its form and by the behavior of the neural crest arising from it. The 

 second landmark is the midbrain, which forms the knee of the cranial flexure. 

 Both of these are distinct as early as the 2-somite stage. Other landmarks 

 appearing soon afterward are, to make mention of two, the distinctive 

 behavior of the neural crest of the trigeminal segment and the unmistakable 

 form and behavior of the cells of the first somite. On the basis of these 

 definite boundaries, a significant interpretation is given of the rhombic and 

 mesencephahc neuromeres. The analysis of Dr. Bartelmez clearly establishes 

 the hindbrain as the dominant feature of the brain in its earliest stages, and 

 thus places man in harmonj'- with other vertebrates. 



Absorption of Cerebrospinal Fluid into the Venous System. 

 The discovery of the physiological phenomena associated with experimental 

 alteration in the salt content of the blood, referred to in previous reports, and 

 certain new technical procedures, particularly a convenient method of record- 



