404 



THE DEVELOPMENT OF THE CHICK 



the condition found in many mammals, the cortical cords of the 

 birds corresponding to the cortical substance, and the medullary 

 cords to the medullary substance of mammals. The medullary 

 cords are often called phaeochroms or chromaffin tissue on account 

 of the specific reaction of the constituent cells to chromic acid, 

 and their supposed genetic relation to tissue of similar composition 

 and reaction found in the carotid glands and other organs asso- 

 ciated with the sympathetic system. 



Aom 



Man 



pl.c.r. 



Jierfi/; e/ttr- 



Msl^cdJ—^' 



■Kcd.I. 



Jc/r.vc, 



Fig. 231. — Photograph of a cross-section of an embryo of 8 days through the 



ostia tubae abdominaha. 



a. A. S., Neck of abdominal air-sac. O. T. a., Ostium tubse abdominale. 

 M's't.ac, Accessory mesentery, pi. C. r., 1., Right and left pleural cavities. 

 Rec. pn. ent. r., Right pneumato-enteric recess. V. c. a. 1., Left anterior 

 vena cava. R., rib. Other abbreviations as before. 



The embryonic histor}^ has been the subject of numerous 

 investigations, and has proved a particularly difficult topic, if 

 we are to judge from the variety of views propounded. Thus 

 for instance it has been maintained at various times: (1) that 



