176 



HISTOLOGY. 



c .t. 



tr. 



GLOMUS CAROTICUM. 



The glomus caroticum [carotid gland] has' already been described as a 

 knot of blood vessels at the bifurcation of the common carotid artery. 

 It is a reddish body "5-7 mm. long, 2.5-4 mm. broad, and 1.5 mm. thick." 

 Between its thin walled, dilated capillaries there are strands of polygonal 

 cells said to be chromaffine and prone to disintegrate (Fig. 197). Many 



nerve fibers, medul- 

 lated and non-medul- 

 lated, enter the glomus 

 and a few multipolar 

 ganglion cells are asso- 

 ciated with them. In 

 its arrangement of 

 cells and blood vessels 

 it resembles a para- 

 b - v - thyreoid gland, and 

 also the glomus coccyg- 

 eum which is far re- 

 moved from entoder- 

 mal structures. Since 

 the nature of the 

 glomus caroticum is 



e.v. c 



undetermined, the 

 three views regarding 

 it may be mentioned. 

 First, it has been con- 

 sidered derived from 



the nodulus thymicus which is now said to form a parathyreoid gland. 

 Recently it has been found that the 'carotid gland' of Echidna comes from 

 the second pharyngeal pouch, and the non-entodermal origin of the human 

 glomus is not beyond question. Second, it has been considered ganglionic 

 or paraganglionic in nature, so that it is classed with nervous structures. 

 Third, it is considered essentially a vascular formation, containing strands 

 of modified mesenchymal cells. 



DEVELOPMENT AND STRUCTURE OF THE TONGUE. 



The tongue consists of two parts, an anterior and a posterior, which 

 differ in origin and adult structure. Separating the branchial clefts from 

 one another there are columns of tissue known as branchial arches. They 

 come together in the median ventral line to form the floor of the mouth 



FIG. 197. SECTION OP A PART OF THE GLOMUS CAROTICUM OF 



MAN. (After Schaper.) 



b.v., Blood vessels; e.v., efferent vein; tr., trabecula; c.t., con- 

 nective tissue septum. 



