3 66 



THE PERIPHERAL NERVOUS SYSTEM 



typically multipolar cells. Their axons possess a neurilemma sheath but remain 

 non-medullated. 



D. CHROMAFFIN BODIES s SUPRARENAL GLAND 

 Certain cells of the sympathetic ganglia do not form nerve cells but are 

 transformed into peculiar gland cells which produce an internal secretion. The 

 secretion formed by these cells causes them to stain brown when treated with 



chrome salts, hence they are called 

 chromaffin cells. Cells of this type 

 derived from the ganglionated cord 

 of the sympathetic system give rise 

 to structures known as chromaffin 

 bodies. Chromaffin derivatives of 

 the cceliac plexus, together with mes- 

 enchymal tissue, form the anlage of 

 the suprarenal gland, an organ which 

 reaches a relatively large size in hu- 

 man embryos. 



The Chromaffin Bodies of the 

 ganglionated cord are rounded cellu- 

 lar masses partly embedded in the 

 dorsal surfaces of the ganglia (Fig. 

 348). At birth they may attain a 

 diameter of 1 to 1.5 mm. In num- 

 ber they vary from one to several 

 for each ganglion. 



Similar chromaffin bodies may 

 occur in all the larger sympathetic 

 plexuses. One of these, associated with the intercarotid plexus, is the carotid gland, 

 which is thus regarded as a derivative of sympathetic chromaffin tissue. The anlage 

 has been first observed in 20 mm. embryos. The largest of these structures found 

 in the abdominal sympathetic plexuses are the aortic chromaffin bodies. These 

 occur on either side of the inferior mesenteric artery ventral to the aorta and 

 mesial to the metanephros. At birth they attain a length of 9 to 12 mm. and 

 are composed of cords of chromaffin cells intermingled with strands of connective 

 tissue, the whole being surrounded by a connective tissue capsule. After birth 

 the chromaffin bodies degenerate but do not disappear entirely. 



Fig. 348. — Section through a chromaffin body 

 in a 44 mm. human embryo (after Kohn). p, p, 

 mother chromaffin cells; sy, sympathetic cells; b, 

 blood-vessel. 



