430 TEXT-BOOK OF EMBRYOLOGY. 



continuation of the internal (membranous and prostatic) portion of the urethra. 

 The genital swellings also fuse and form the scrotum, the line of fusion in the 

 medial line becoming the raphe (Fig. 386). Primarily the inguinal ligaments 

 of the mesonephroi are attached to the corium of the skin in the genital swellings, 

 and as the testicles descend they pass through the inguinal ring into the scro- 

 tum. In a sense the scrotum represents an evagination of the body wall 



THE DEVELOPMENT OF THE SUPRARENAL GLANDS. 



Although the suprarenal glands do not logically come under the head of the 

 urogenital system, being neither functionally nor developmentally a part of the 

 latter, it is most convenient to consider them in this chapter. 



In Mammals including man these glands are composed of two parts which 

 can be differentiated histologically and topographically — the cortex and 

 medulla. The cortex is composed of trabecule and spheroidal masses of cells 



Phaeochrome cells 



Nerve fibers 



PhcBochrome Connective Sympathetic 



cells tissue ganglion cells 



Fig. 387. — Section of a sympathetic ganglion in the cceliac region of a frog (Rana esculenta), 

 showing differentiating phaeochrome cells. Giacomini. 



which do not have a strong affinity for the ordinary cytoplasmic stains and 

 which contain granules of a fat-like substance known as lipoid granules. The 

 medulla is composed of irregularly arranged sympathetic ganglion cells and 

 other granular cells which, after treatment with chrome salts, acquire a peculiar 

 brownish color. The brown cells are known as chromaffin (or phaeochrome) 

 cells and their granules as chromaffin (or phaeochrome) granules. As cortex 

 and medulla are distinct anatomically, they are also distinct developmentally, 

 being derived from two distinct and different parent tissues which unite 

 secondarily. Furthermore, it is an interesting fact that in the lower Vertebrates 

 (Fishes) the two parts remain permanently separate; that in the ascending 

 scale of animal life (Amphibia, Reptiles, Birds) they become more closely 

 associated; and that finally (in Mammals) they unite to form a single glandular 

 structure. In Mammals the phylogenetic history is repeated with remarkable 



