EMBRYOLOGY OF TADPOLE AND CHICK 



583 



passes under the eye to the snout. It is innervated by the buccalis nerve 

 which is a branch of VII. ';.'*' 



(3) The hyomandibular line runs along the jaw and operculum. 

 This is innervated by twigs from the mandibularis externus, and finally, 

 (4) the lateral line proper, which may be double. This extends back to 

 the tail on both sides of the animal, being innervated by twigs from the 

 lateralis, a branch of the X cranial nerve. 



Fig. 340. 



The development of the lateral line organs in R. sylvatica. A. Part of a 

 frontal section through the level of the ndtochord of a 3.3 mm. embryo. B. Part 

 of a transverse section through the vagus region of a 4 mm. embryo. C. Part 

 of a frontal section through a 4 mm. embryo of R. virescens. D. Section through 

 the lateral line organ of a 15.5 mm. larva of R. sylvatica. a. Auditory vesicle (in 

 A, its rudiment) ; 6, basement membrane of epidermis; eh, notochord ; g, gut; gV, 

 trigeminal ganglion, of V cranial nerve; gVlll, acoustic ganglion of VIII 

 cranial nerve ; gX, vagus ganglion ; gXl, ganglion of the lateral nerve (branch of 

 the vagus) : t, intersegmental thickenings of the epidermis (ectoderm) ; I, rudi- 

 ment of lateral line nerve ; lp, lateral plate of mesoderm ; my, myotomes ; n, inner 

 or nervous - layer of epidermis (ectoderm) ; nc, nerve cord; p, pigment in epi- 

 dermis ; si, inner sheath cells of lateral line organ ; sn, sensory cells of lateral 

 line organ ; so, outer sheath cells of lateral line organ. . K, Lateral line canals 

 and their nerves in a pollack (a fish belonging to the cod group). Canals and 

 brain are dotted while the lateral nerves are black, b, buccalis ramus of the 

 VII nerve; dl, dorsal rarnu* of lateralis of X nerve; h, hyomandibularis nerve; 

 Km, hyomandibular line of organs; to, infraorbital line; 1, lateral-line canal; n, 

 nares ; o, olfactory lobe ; op, operculum ; os, ophthalmicus superncialis nerve ; aoc, 

 commissure which connects the lines of both sides; so, supraorbital line of organs; 

 st, supratemporal part of lateral line vl, ventral- ramus of lateralis of X nerve ; 

 *, visceralis portion of X nerve. '(A. to D, from Harrison; E, from Kingsley after 

 Cole.) 



