76 



CRANIAL NERVES. 



epiblast into rudiments of special sense organs, which become gradually shifted 

 doAvnwards and outwards away from the ganglion rudiments, and form the so-called 



KTtlC 



Fig. 88. TRANSVERSE SECTION THROUGH THE ANTERIOR PART OP THE TRUNK OF AN EMBRYO OF 



SCYLLIUM. (Balfonr. ) 



sp.c, spinal cord ; sp.y, ganglion of posterior root ; ar, anterior root ; dn, dorsal ; sp.n, ventral 

 branch of spinal nerve ; mp, muscle plate ; mp', part of muscle plate already converted into muscle ; 

 mp.l, part of muscle plate extending into the limb ; nl, nervus lateralis ; ao, aorta ; ch, notochord ; 

 sy.g, sympathetic ganglion ; ca,v, cardinal vein ; sd, segmental duct; st, segmental tube ; du, duode- 

 num ; hp.d, junction of hepatic duct with it ; pan, rudiment of pancieas connected with another part 

 of duodenum ; umc, opening of umbilical canal (vitelline duct). 



" branchial sense-organs " of Beard. They become connected subsequently with 

 outgrowths from the posterior nerve-rudiments. 



These rudimentary sense organs have been described in mammals also (by Froriep). They 

 appear to represent the special sense organs of the gill clefts of fishes, which were first de- 

 scribed by Leydig (1850). Beard is of opinion that the nose and ear are also specialised 

 branchial sense organs, the only ones that are persistent in higher vertebrates. This 

 differentiation of a special sensory portion of epiblast into rudiments of special sense- 

 organs, occurs according to Golowine's observations in the chick, not only in the head but also 

 in the trunk, where they in all probability represent rudiments of " organs of the lateral line," 

 such as are seen in fishes. 



Various observers have described the ganglion rudiments as actually becoming formed at 



