SENSORY CANALS OF THE COMMON SKATE. 103 



~L.lp.lc, The lateral canal. lp., the most anterior part continuous with the otic portion of infra-orbital ; 

 lc., the commissure connecting the two canals ; L., the anterior portion of the trunk canal — the 

 tubules are shown on right of figure ; I., the lateralis nerve arising above the level of the glosso- 

 pharyngeal nerve ; l.gl., the ganglion of the lateralis ; I. 1 , the first branch passing to the sense organs 

 of the commissure and the precommissural part of the lateral canal — this branch may contain 

 some glossopharyngeal fibres ; I. 2 , the second branch supplying sense organs of anterior part of 

 trunk canal; n.a., nasal aperture; E., eye; sp., spiracle; mo., mouth; l.f., labial fold ; a.p., auditory 

 pores ; fa., facial nerve — the homologue of facial in higher vertebrates ; pi., its palatine branch ; 

 ps., pre-branchial, and p.b., post-branchial branches; s./.,the most superficial root fibres of facial, 

 some of which pass to all three supra-branchial nerves — these fibres probably innervate the 

 ampullae of the ampullary canals ; v.gl., large ganglion of vagus with which the branchial branches 

 (b^-b. 4 ) and the intestinal branch are connected. 



PLATE II. 



Fig. 2. Diagram to indicate the distribution of the dorsal branches of the cranial nerves. Pr., Ophthalmicus 

 profundus, springing from brain in front of the trigeminal (Tr.) ; o.n., root of profundus (oculo- 

 nasal) ; o.n.g., ganglion of profundus ; o.n. 1 , dorsal branch of profundus ; I.e., long ciliary branches ; 

 or., orbital branch ; l.r., long root of ciliary ganglion ; o.m., deep branch of oculo-motor giving off 

 short root (s.r.) of ciliary ganglion (e.g.) ; s.c., short ciliary nerves passing to eyeball. 



Tr., Trigeminus, t.r., trunk of trigeminus near Gasserian ganglion (G.) ; s.o.t, dorsal or superficial 

 ophthalmic branch of trigeminus ; mx., maxillary (pre-branchial) branch ; mi, mandibular (post- 

 branchial) branch ; mo. , mouth. 



Fa 1 ., Four roots, the fibres of which are rearranged to form the three supra-branchial branches 

 of the facial (the superficial ophthalmic, buccal, and hyomandibular), which innervate the five 

 groups of ampullae, and the supra-orbital, infra-orbital, and hyomandibular sensory canals. 



Fa., Root of the nerve which corresponds to the facial of higher vertebrates. It lies in contact 

 with, and receives a communicating branch from, the auditory nerve (Am.). 



s.o.f., The first dorsal branch of facial — the ophthalmicus superficialis — which supplies the supra- 

 orbital canal (S.O.), the superficial ophthalmic group of ampullae (S.O.A.). s.o.f. 1 , the ganglion; 

 s.o.f. 2 , the ventral branch passing to the terminal portion of the supra-orbital canal (S.O.). 



bu., The second dorsal branch of facial — the buccalis — which supplies the infra-orbital canal (I.O.), 

 and the inner (LB. A.) and outer (O.B.A.) buccal groups of ampullae. bu., the ganglion on 

 the buccal nerve, from which a branch springs to supply the proximal part of the infra-orbital 

 canal ; bu. 1 , the inner division of the buccal which innervates the inner buccal group of ampullae 

 (I.B.A.) and the greater part of the infra-orbital canal beyond its connection with the supra- 

 orbital ; bu. 2 , the outer division of the buccal which supplies part of the infra-orbital canal and 

 the outer buccal group of ampullae (O.B.A.); km., the third dorsal branch of facial — hyomandi- 

 bularis — which innervates the hyoid and mandibular groups of ampullae, and the hyomandi- 

 bular canal, including the ventral loop, the dorsal extension, and the mandibular part, when 

 present; h.g., the ganglion of the hyomandibular lying in contact with the ganglion of the 

 facial proper (fa.); hm. 1 , the large branch for the hyoid group (HA.) of ampullae; hm?, the 

 branch which supplies the mandibular group of ampullae (M.A.), and the mandibular canal (m.c.) — 

 the mandibular offshoot and the mandibular group of ampullae are both absent in Laemargus ; 

 sp., spiracle. 



fa., The homologue of the facial of higher vertebrates, pi., palatine which passes from the ganglion 

 to roof of mouth; p.s., pre-branchial fibres to the spiracle ; p. b., post-branchial branch which 

 passes behind spiracle, and eventually reaches the mucous membrane over the hyoid arch; m.f, 

 motor fibres which leave this nerve to supply some of the jaw muscles. 



Aw., The auditory nerve passing to the auditory apparatus (A.A.). a., auditory pore; GL, glosso- 

 pharyngeal nerve arising under cover of the lateralis; gl., its ganglion, beyond which are the 

 pharyngeal pre- and post-branchial branches ; gl., the dorsal branch represented as supplying 

 VOL. XXXVII. PART I. (NO. 6). R 



