74 E. V. COWDEY 



carotid body developed from the epithelium of the branchial cleft and 

 regarded it, therefore, as a gland. His recognition that the epithelium 

 seemed to disappear in the later stages of development, however, later led 

 him to doubt this conclusion. It has since been abundantly shown that 

 the organ is not of epithelial origin. 



Histology. The characteristic cells of the carotid body are arranged 

 in spheroidal clumps, imbedded in connective tissue. Kohn(a) has placed 

 them in four groups, depending upon the density of the parenchyma : 



Cell Types. Compact Type. This consists of a single mass re- 

 sembling a ganglion. It is with difficulty penetrated by a needle and is 

 found in the cat. 



Intermediate Type. This group is not so compact .as the preceding, 

 nor so diffuse as the following. It is found, for example, in. the ape. 



Granular Type. This is composed of scattered cell groups, as in man. 



Diffuse Type. This is sufficiently described by the name. It is found 

 in the rabbit. 



Schaper showed that the characteristic cells of the organ are neither 

 gland cells, as earlier claimed, nor endothelium from the vessel walls. He 

 disputed the claim that they are merely rudimentary structures, and sug- 

 gested that they have some definite function. 



Chromaphil Reaction. By the application of chromium salts Stil- 

 ling^) showed that, as a matter of fact, the cells are of the same chroma- 

 phil type as those found in the paraganglia and the suprarenal medulla. 

 He therefore designated the body a vascular gland analogous to the supra- 

 renals. That the tissue in question is similar to that of the medulla was 

 further shown by Mulon(e), in that extracts of the carotid body give a 

 pressor vasomotor reaction, similar to that of epinephrin. 



The Coccygeal Bodies 



The coccygeal bodies are small masses of tissue, the largest of which 

 rarely exceeds three millimeters in diameter. They are usually of spher- 

 ical or lobulated shape, of a reddish color, and are situated immediately 

 ventral to the end of the coccyx. The middle sacral artery is the best 

 clew to their location (Fig. 9). They are highly vascular and are richly 

 supplied with sympathetic fibers. 



When the coccygeal bodies were first discovered by Luschka(a), he 

 regarded them as ductless glands which had developed in part from the 

 sympathetic nervous system. Stork has shown that this conception is 

 quite erroneous, and that neither in fetal nor post-fetal life do the bodies 

 give the characteristic chromium reaction. Schumacher has afforded con- 

 clusive evidence that the coccygeal bodies correspond to the glomeruli 

 caudales of lower forms, which are developed as arteriovenous anastomoses. 



