ANATOMY, EMBEYOLOGY AND HISTOLOGY 73 



nature. The blood in the suprarenal veins contains epinephrin and 

 exhibits u green coloration with sesquichlorid of iron (Vulpian's reaction). 



THE CAROTID AND COCCYGEAL BODIES 



Strictly speaking, the carotid body is merely an outlying portion of 

 the suprarenal system proper, and might well be treated in connection 

 with the accessory suprarenals and paraganglia. The coccygeal body, on 

 the other hand, has apparently no relation to the suprarenals. Since 

 Luschka's first description of them they have been conventionally treated 

 together, however, and, as a matter of convenience, the two structures may 

 be discussed in this place. 



The Carotid Bodies 

 Anatomy 



Gross Morphology and Relations. The carotid bodies are small oval 

 structures of a reddish color, about six millimeters long and two milli- 

 meters thick, situated near the bifurcation of the common carotid arteries. 

 They are subject to considerable variation, and may be absent or so small 

 as to escape detection. Frequently a gland is divided into two unequal 

 parts, which are confluent below. It may be broken up into four or five 

 parts. Each gland possesses a capsule bound down by connective tissue 

 to the wall of the artery, which is slightly thickened at the point of con- 

 tact. The body has a very rich vascular and nerve supply, the latter 

 chiefly sympathetic, though it has been claimed, probably erroneously, that 

 the glossopharyngeal, superior laryngeal, and hypoglossal nerves con- 

 tribute fibers to it. Ganglion cells are found in the bundle of nerve fibers. 



Embryology and Phylogeny. Both ontogenetically and phylogenet- 

 ically the carotid bodies are clearly composed of chromaphil tissue. Their 

 development in man has not been carefully worked out. It has been 

 found, however, that they are formed from sympathochromaffin tissue, 

 which accumulates on each side of the body in the vicinity of the internal 

 carotid artery, near the ganglion nodosum of the vagus. They have been 

 found in most mammals which have been investigated. We regard them 

 as vestiges in man of the chromaffin tissue which is relatively more highly 

 developed in lower forms and, as such, they are comparable to the para- 

 ganglion aorticum. Luschka(fr), wno fi rst recognized the gland as an en- 

 tity, interpreted it as a "nerve gland," auxiliary to the sympathetic system. 

 Shortly afterward, Arnold, as a result of further study, came to the 

 conclusion that it is merely a network of blood vessels, the walls of which 

 are composed of extra layers of epithelium. Stieda believed that the 



