SENSORY CANALS OF THE COMMON SKATE. 



105 



passing to outer buccal group of ampullar; O.B.A., part of the dorsal and part of the ventral 

 portion of the infra-orbital canal ; bu.\ inner division of buccal passing to inner buccal group of 

 ampullae and the infra-orbital canal from its junction with the hyomandibular. 

 HM.-HM. 7 , Hyomandibular canal. HM., canal communicating with the infra-orbital (I.O. 5 ) ; 

 HM. 1 , end of ventral loop ; HM. 2 , outer limb of loop bends inwards ; HM. 3 , canal passing to 

 dorsal surface ; HM. 4 , canal as it reaches dorsal surface ; HM. 5 , expanded part communicating 

 with tubules of infra-orbital ; HM. 5 -HM. 6 , long dorsal extension which terminates in scapular 

 offshoot from lateral canal ; HM. 7 , mandibular portion of hyomandibular canal ; t. n , t. 15 , t. bi , t. 67 , 

 tubules ; km., hyomandibular nerve ; hm.g., its ganglion ; hrn. 2 , branches passing in front of or 

 through the hyoid group of ampullae (H.A.) to innervate the sense organs of the various parts of 

 the hyomandibular canal, with the exception of the mandibular portion ; lirn. 1 , branch for the 

 mandibular group of ampullae (M.A.) and the mandibular portion (HM. 7 ) of the hyomandibular 

 canal. 

 L.-L. 3 , The lateral canal, l.p., the precommissural part, and I.e. the commissural part, of lateral 

 canal ; sc, scapular offshoot ; p.sc, post-scapular offshoot ; p.o. 1 , lateral row of pit organs ; p.o., 

 pit organs near the auditory pore (a.). 

 l.-l. 2 , Lateralis nerve, l.g., its ganglion ; l.t., branch which innervates half of commissure (I.e.), part of 

 lateral canal in front of commissure (l.p.), and anterior part of main canal ; l.sc, branch for scapular 

 offshoot (se.) ; l.p.sc, branch for post-scapular offshoot ; Z.M. 2 , lateralis giving off branches to sense 

 organs of lateral canal posterior to shoulder girdle. 



Fig. 6a. Transverse section through snout of young (just hatched) R. batis. S.O., supra-orbital canal 

 (rostral part); S.O. 1 , ventral part of the same canal (subrostral) ; I.O., infra-orbital canal (prenasal 

 part) ; r., cartilage of rostrum ; a.c, ampullary canals from superficial ophthalmic group of 

 ampullae ; g.e., goblet cells of skin. 

 Transverse section through lateral canal of a young (just hatched) R. batis, showing the thick 

 cartilaginous lateral walls, and thin roof and floor, s.o., the sense organ on inner wall of canal ; 

 g.c, goblet cells of skin, x 120. From a photograph. 

 Transverse section through a ventral subcutaneous canal (ventral part of supra-orbital), showing the 

 large sense organ (s.o.) lying in the roof of the canal, and some of the connective tissue in which 

 the canal is embedded, x 300. From a photograph of a section of a R. batis 1 6 '5 cm. long. 



Fig. 10. Transverse section through a pit organ, showing the sense organ at the bottom of the involution. 

 From near root of tail of a young R. batis. 



Fig. 8. 



Fig. 9. 



