406 THE DEVELOPMENT OF THE CHICK 



however, no capsule is formed yet. The topography of the organ 

 on the eighth day is shown in Figs. 150 and 182. Whereas during 

 the fourth, fifth, and sixth days the arrangement of the cortical 

 cells is in masses rather than in cords, on the eighth day the 

 cords are well developed, in form cylindrical with radiating cells, 

 but no central lumen. The organ has become vascular, and the 

 vsesels have the form of sinusoids, i.e., they are moulded on the 

 surface of the cords with no intervening mesenchyme. 



Origin of the Medullary Cords. The medullary cords take 

 their origin unquestionably from cells of the sympathetic ner- 

 vous system. During the growth of the latter towards the mesen- 

 tery, groups of sympathetic cells are early established on or near 

 the dorso-median surface of the cortical cords (Fig. 226). The 

 ingrowth of the sympathetic medullary cords does not, however, 

 begin until about the eighth day. At this time there is a large 

 sympathetic ganglionic mass on the dorso-median surface of the 

 anterior end of the suprarenal, and stands of cells characterized 

 sharply by their large vesicular nuclei and granular contents 

 can be traced from the ganglion into the superficial part of the 

 suprarenal. These cells are precisely like the specific cells of 

 the ganglion, perhaps a little smaller, and without axones. On 

 the eleventh day these strands have penetrated through a full 

 third of the thickness of the suprarenal, and are still sharply 

 characterized, on the one hand by their resemblance to the sym- 

 pathetic ganglion cells, and on the other by their clear differen- 

 tiation from the cells of the cortical cords. These occupy the 

 relations characteristic of the differentiated medullary cords, and 

 there can be little doubt that they develop into them. 



