THE CELL CLUSTERS IN THE DORSAL AORTA 

 OF MAMMALIAN EMBRYOS^ 



V. E. EMMEL 



Assistant Professor of Anatomy, University of Illinois, College of Medicine 

 From the Department of Anatomy, Washington University Medical School 



TWO PLATES (11 figures) 



CONTENTS 



I. General structural characteristics of the aortic cell clusters 401 



II. The question of their origin 402 



1. Statement of problem 402 



2. Grounds for regarding these clusters as of greater significance than 



merely incidental structures 403 



3. Evidence as to their origin from the vascular endothelium 405 



III. Concerning the correlation of the clusters with certain aortic develop- 

 mental processes 407 



1. Degeneration and caudal wandering of aortic rami 407 



2. Correlation of the aortic clusters with these vascular changes ... 409 

 IV. Discussion concerning endothelial tissue as contributing to the cellular 



elements of the blood 412 



V. Resume 413 



VI. Literature cited 415 



I. GENERAL STRUCTURAL CHARACTERISTICS OF THE AORTIC 



CELL CLUSTERS 



Figure 1 represents a portion of the ventral wall of the dor- 

 sal aorta as seen in a median sagittal section of a 9 mm. pig 

 embryo. Along its endothelial surface may be observed five 

 or six darkly stained cellular masses or clusters (aci-aCo). Fig- 

 ures 2, 3 and 4 represent similar clusters as seen in transverse 



1 Some of the present observations were made while engaged in research work 

 at the University of Strassburg and I wish here to express my indebtedness to 

 Professor Weidenreich for the generosity with which the facilities of his labo- 

 ratory were placed at my disposal. An abstract of the work was also published 

 in the Proceedings of the American Association of Anatomists, Anatomical 

 Record, Vol. 9, p. 77, 1915. 



401 



THE AMERICAN JOURN.\I, OF .VNATOMY, VOL. 19, NO. 3 



