368 THE PERIPHERAL NERVOUS SYSTEM 



with the semilunar ganglion by two communicating rami. The submaxil- 

 lary ganglion is intimately related through the mandibular division of the 

 trigeminal nerve to the semilunar ganglion, while the otic ganglion is 

 united to the latter by a plexus and is related to the glossopharyngeal nerve 

 through its tympanic branch. 



The cervical ganglia lose their segmental arrangement and represent 

 the fusion of from two to five ganglia of the cervical and upper thoracic 

 region. The more distally located prevertebral ganglia (of the cardiac, 

 cceliac, hypogastric, and pelvic plexuses) are derived from cells of the neural 

 crest which migrate to a greater distance ventrally (Fig. 366). The vis- 

 ceral ganglia (of the myenteric and submucous plexuses, and the preverte- 

 bral cardiac plexus as well, are derived by Kuntz chiefly from migratory 

 cells from the hind-brain and from the vagus ganglia. 



The sympathetic nerve cells give rise to a^ons and dendrites, and are 

 thus typically multipolar cells. Their axons possess a neurilemma sheath, 

 but remain unmyelinated. 



D. THE CHROMAFFIN BODIES AND SUPRARENAL GLAND 



Certain cells of the sympathetic ganglia, instead of becoming neurons, 

 are transformed into peculiar gland cells ; these produce an important inter- 

 nal secretion which affects the blood pressure. 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 mesenchymal tissue, also form the anlage of the suprarenal 

 gland. 



The Chromaffin Bodies of the ganglionated cords are rounded, cellular 

 masses partly embedded in the dorsal surfaces of the ganglia (Fig. 367). 

 At birth they may attain a diameter of i to i . 5 mm. In number they vary 

 from one to several for each ganglion. 



Similar chromaffin bodies may occur in all the larger sympathetic 

 plexuses. The largest of these structures, found in the abdominal sym- 

 pathetic plexuses, are the aortic chromaffin bodies (of Zuckerkandl) . 

 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 con- 

 nective-tissue capsule. After birth the chromamn bodies degenerate, but 

 do not disappear entirely. 



