Proceedings of the Association of American Anatomists 513 



For the study of nuclear changes during histogenesis there is probably 

 no cell more suitable than the striated muscle cell, since it is here pos- 

 sible to determine, not only volumetric relations, but also periods of 

 maximal cytoplasmic activity as revealed by fibrillation. The investiga- 

 tions have led to the following tentative conclusions: the nuclei un- 

 dergo striking changes in position, in that they migrate to areas of accel- 

 erated cytoplasmic activity. 



The amount of chromatin in a given nucleus is increased pari passu 

 with increased cytoplasmic activity. Further, it becomes vmequally 

 distributed in the nucleus, showing "a marked condensation on the side 

 which is applied to the fibrillated tract. This increase in the amount 

 of chromatin is to be interpreted as an elaboration of nuclein which is 

 given off and later finds its way into the dark band of the fibril. 



In the earliest phases of differentiation a unit of nuclear material is 

 in physiological equilibrium with two to three units of cytoplasmic 

 material, while in the adult a unit of ni^clear material is equilibrated 

 with twenty to thirty units of cytoplasmic material. Before regenera- 

 tion is possible, this disproportion is corrected by an increase in the 

 amount of nuclear material. 



Nuclear differentiation accompanies cytoplasmic differentiation, the 

 nuclei of the different tissues showing structural and chemical differ- 

 ences. ■ ' 



THREE ANOMALIES OF THORACIC BLOOD-VESSELS. By Valray P. 

 Blair. 



1. Anomalous Pulmonary Vein. — This was observed in an adult male 

 who died of pneumonia. No other history obtainable. The anomaly is 

 a vein arising from the superior lobe of the left lung near its root. 

 Its size is little less than that of an ordinary pulmonary vein. It empties 

 into the left brachio-cephalic vein. The vein could be traced almost 

 down to the base of the lobe running in the substance of the lung near 

 the mesio-ventral border. It seems to be a true pulmonary vein and 

 its capacity would indicate that about one-sixth of the blood was re- 

 turned from the lung to the right side of the heart. (A description of 

 this anomaly will appear in the Medical Bulletin of the Washington 

 University, St. Louis.) 



2 and 3. Anomalous Subclavian Arteries. — In both instances the 

 right subclavian artery had its origin from the left side of the arch of 

 the aorta, the one from the convexity, the other from the concavity of 

 the arch. 



