THE DEVELOPMENT OF THE AKM IN MAN. 



BY 



WARREN HARMON LEWIS, M. D. 



Instructor in Anatomy, The Anatomical Laboratory, Johns Hopkins University. 



With 3 Plates and 14 Text-Figures. 



The wandering of the trapezius and the latissimus dorsi and also of 

 muscles in the ahdominal wall was noted by Dr. Mall ' several years 

 ago. At his suggestion I undertook, in the spring of 1897, a more 

 careful study of these and other changes in the development of the arm 

 region in man. Similar studies were undertaken later by Dr. Bardeen 

 on the leg and body wall. We have embodied many of the important 

 points obtained from our studies in a joint article ^ which appeared in 

 the first number of this journal, and of which this present article may 

 be considered a continuation. 



In the present paper I purpose to consider the origin of the tissue 

 which fills the arm bud, the entrance of nerves into this tissue and its 

 differentiation into skeleton, ligaments, muscle and tendon, and finally 

 the growth and wandering of these structures until practically the adult 

 conditions are present. 



I wish here to express my most sincere thanks to Dr. Mall for his 

 constant interest and many suggestions, and also for the use of the 

 valuable embryological material in this laboratory. 



The embryos studied, with the exception of the one belonging to 

 Dr. Buxton, of Cornell University, are in the collection belonging to 

 Dr. Mall. Most of those considered in this paper are tabulated on 

 page 2, Vol. I, of this journal. 



From the serial sections of embryos CLXIII, CIX, XLIII and XXII 

 I have made reconstructions of the arm region after the Born method. 

 The arm region in Plates III to IX in the paper by Bardeen and Lewis 



' Mall, Development of the ventral abdominal walls in man. Jour, of Morph., 

 Vol. XIV, 1898. 



2 Bardeen and Lewis, Development of the limbs and body wall in man, Am. Jour, 

 of Anat., Vol. I, p. 1. 



