n8 NORMAL HISTOLOGY. 



The latter are irregularly disposed as clumps or cell-balls and occupy the 

 interspaces within the close network of large capillaries which ramify among 

 the cells. The characteristic elements of the carotid body are the polygonal 

 cells, about 10 A in diameter, with large round nuclei. Their protoplasm is 

 finely granular and is especially prone to change, being best preserved in 

 solutions of chromic acid salts. 'When so treated, they take on the peculiar 

 yellow color entitling them to be classed as chromaffine cells. The large 

 number of nerve-fibres within the carotid body is remarkable. They are 

 mostly nonmedullated and are derived chiefly from the neighboring sympa- 

 thetic plexus surrounding the carotid artery. After entering at different 

 places, they ramify within the organ in all directions, the finest filaments 

 being lost among the groups of cells. The penetrating nerve-trunks usually 

 enclose typical ganglion-cells and, in a sense, the chromaffine cells likewise, 

 since the nerve-fibres surround the groups of these elements. 



In view of (i) the identity of its elements with other chromaffine cells, 

 which are now recognized as closely associated with the sympathetic system 

 in other localities, as in the medulla of the suprarenal body, (2) its extraor- 

 dinary richness in nerve-fibres, (3) its general resemblance to a sympathetic 

 ganglion, and (4) its arly development from embryonal sympathetic gan- 

 glion-cells, Kohn concludes that, since the carotid body is neither a gland nor 

 a typical ganglion, it must be regarded as accessory to the sympathetic 

 system and, in recognition of this relation, proposes the name paraganglion 

 caroticum for the organ. Concerning its function nothing is definitely 

 known; possibly this depends upon adrenalin from the chromaffin tissue. 



The blood-vessels supplying the carotid body are branches which pass 

 directly from either the common carotid artery or its terminal branches. 



THE COCCYGEAL BODY. 



This organ, also often called \.\\& glomus coccygeum, coccygeal gland, or 

 Luschka? s gland, is a small reddish yellow ovoid body which lies embedded 

 in fatty areolar tissue usually immediately in front of the tip of the coccyx, 

 but sometimes just below. The dimensions of the organ are small, its 

 transverse and greatest diameter being from 2.5-3 mm - an d its thickness 

 less than 2 mm. It sometimes is divided into two or even more tiny lobes. 

 The body thus described is, however, only the largest of a series of nodules 

 which includes a variable number of structures, for the most part of minute 

 size, irregularly grouped around the chief mass (Walker). The additional 

 nodules are in many cases connected with the principal body by means of 

 delicate pedicles; in others they are entirely free, but in all instances they 

 are grouped around the middle sacral artery or its branches. 



The body, as seen in transverse sections (Fig. 158), includes an irreg- 

 ularly oval field of connective tissue, fairly well defined from the surrounding 

 fatty areolar tissue, in which are enclosed numerous aggregations of epi- 

 thelial cells and, sometimes, a thick-walled artery. The proportion of cell- 

 masses to the connective-tissue stroma varies, in some cases the cellular 

 constituents predominating, but commonly the fibrous stroma being the more 

 bulky. The individual cell-groups are uncertainly circumscribed by a slight 

 condensation of the surrounding fibrous stroma. Each aggregation of cells 

 contains a central blood-space, limited by an endothelial wall similar to that 

 of a capillary. Against this wall the epithelial cells lie without the interven- 

 tion of connective tissue; likewise the cells themselves are closely packed in 

 direct apposition with one another and in consequence present a polygonal 



