THE CAROTID GLAND 



569 



as the original source of leukocytes. The proliferative foci are the cortical 

 portions of the lobules; the medulla does not correspond to the germ cen- 

 ters of lymph nodules, but is probably an area of leukocyte dissolution. 

 The thymus does not seem to be an organ essential to life. Extirpation in 

 dogs and guinea pigs is not followed by death. However, the experimental 

 evidence indicates a reciprocal functional relationship between the thymus 

 and certain of the organs of internal secretion, especially the sex-glands. 

 This suggests a secretory role; a conclusion supported by the results of 

 the recent experiments of Gudernatsch (Amer. Jour. Anat., 15, 4, 1914) 

 in which thymus fed to frog tadpoles, accelerated growth, but suppressed 

 differentiation. 



V. THE CAROTID GLAND 



.. .- Qfl. 



' . . 



.- 



. 



This body was first carefully described by Luschka (1862) and, 

 from its intimate relation to the blood-vessels and nerves, is also known 

 as the glomus caroticum or ganglion inter caroticum. It is about the 

 size of a rice grain. It 

 consists of scattered 

 masses of epithelioid cells, 

 usually grouped in small 

 splieroidal clumps or 'cell 

 lulls' embedded in the ; 



connective tissue at the 



(% * ' . ' ' . " *^ 



m/' 



-' ' -\ . 

 ! .-./ . 



. . "," 



.'. . 



/ -'. ' -* 



clirg '" 



FIG. 489. CAROTID GLAND OF AN APE. 



Chrg, a 'chromaffin cell'; .s, connective tissue 

 septum. Portions of two adjacent lobules are in- 

 cluded in the figure. X 200. (After Kohn.) 



> ^ - ' . - 



. . - . "-*.? 



.-...'- -- v 



. 





*/ 



.., \ -' ' ^ 



point of bifurcation of the 

 common carotid artery. 

 Kohn (Arch. f. Mik. 

 Anat,, 1900) has de- 

 scribed four types of the 

 gland according to the 

 density of its parenchyma 

 the type found in man 

 consists of scattered cell 

 groups; in the rabbit they 



are even more diffuse. The carotid gland of a cat consists of a single cell 

 mass, while that of the ape is intermediate between that of the cat 

 and man. 



The glandular elements are derived from embryonal sympathetic 

 ganglion cells (Kohn). They are ovoid cells with finely granular 

 cytoplasm and a spheroidal, somewhat vesicular nucleus. Many of them 

 contain chromaffin granules. Because of its genetic relationship and 



