104 PROFESSOR J. C. EWART AND MR J. C. MITCHELL ON THE 



(1) a short segment (T.T.) of the great longitudinal canal immediately behind the infra-orbital 

 canal, and (2) a row of pit organs (p.o.). That the dorsal branch of the glossopharyngeal 

 innervates sense organs and pit organs in Selachian as in Amia has not yet been demonstrated. 



T.T., The part of the longitudinal canal which the glossopharyngeal might be expected to innervate 

 in a typical Selachian. This might be known as the glossopharyngeal or temporal canal. 1 br., 

 first (glossopharyngeal) branchial cleft. 



La., Lateralis nerve, l.g., lateralis ganglion ; I. 1 , first branch passing to the temporal commissure 

 (Lc), and the anterior part of the lateral canal (L.). 



I. 1 , Branch springing from the ganglion to supply part of the canal and the anterior follicles or pit 

 organs (p.o.l.). l.n., the lateralis extending backwards, nearly parallel with the lateral canal (L.). 



W-V. 3 , The first three branchial branches of the vagus, each with a ganglion (II.-IV.), pharyngeal 

 pre- and post-brauchial branches. 



V. 4 -V. 5 , The united fourth branchial and intestinal branches of vagus. V., ganglion of vagus IV. ; 



i.gl., ganglion at root of intestinal branch (i.n.) ; 2 br.-5 br., second to fifth branchial (vagus) clefts. 



Fig. 3. The Cranial Canals of Amia. This figure has been introduced to admit of a comparison between 



Amia and Selachians, and to indicate the new system of grouping the canals. The details are 



from a figure by Allis (30), with which it should be compared. 



S.O., Supra-orbital canal, s.o.f., superficial ophthalmic of facial supplying the canal and a row of 

 pit organs (s.p>). 



I.O., Infra-orbital canal, ot.n., the otic branch of facial which supplies the sense organs 15 and 16 

 of the first segment {ot. ot. 1 ) of the infra-orbital ; bu., the buccal nerve supplying the infra- 

 orbital canal, with the exception of the otic part. HM., the hyomandibular canal extending 

 downwards from the proximal end of the infra-orbital to run along the mandible ; hm., the 

 hyomandibular nerve supplying the hyomandibular and four rows of pit organs. 



T., Temporal canal lying between infra-orbital and lateral, gl. 1 , glossopharyngeal nerve supplying 

 the single sense organ of the temporal canal and a row of pit organs ; gl., ganglion of glosso- 

 pharyngeal nerve. 



L., Lateral canal beginning at the posterior end of the temporal and extending on to the trunk. 

 I.e., supra-temporal commissure ; L, lateralis nerve ; I. 1 , first branch supplying commissure, a line 

 of pit organs, and two sense organs of the main canal ; I?, second branch supplying a sense organ 

 and a row of pit organs {p.o.) ; I. 3 , a third branch supplying the sense organ (21), which, according 

 to Allis, lies at the junction of the infra-orbital and lateral canals. 

 Figs. 4 and 5. Sensory Canals of Chlamydoselachus (after Garman). cr., r., sr. =* supra-orbital canal; orb., on., 

 n., pn. = infra-orbital ; oc, au. = precommissural and commissural parts of lateral canal (/.); ang., 

 angular; /., jugular; o., oval ; g., gular ; sp., spiracular — part of hyomandibular canal. 



PLATE III. 



Figs. 6 and 7. Sensory Canals of Rata batis. S.O.-S.O. 3 , Supra-orbital canal. S.O., proximal part ; S.O. 1 , 

 beginning of rostral portion; S.O. 2 , point where canal penetrates snout to reach ventral aspect; 

 S.O. 3 , S.O.*, ventral loop; S.O. 5 , canal joining infra-orbital; t. 7 , t. 23 , t. 33 , t. i5 , tubules. 



s.o.f., Superficial ophthalmic branch of facial with ganglion on root. It supplies supra-orbital canal 

 and the ophthalmic group of ampulla?, v.b., ventral branch passing to sense organs of ventral 

 portion of canal ; S.O. A, positiou of superficial ophthalmic group of ampullae. 



I.O.-I.O. 8 , Infra-orbital canal. I.O., canal continuous with lateral canal and communicating with 

 supra-orbital ; I.O. 1 , sub-orbital portion ; I.O. 2 , canal passing to ventral surface ; I.O. 3 , beginning of 

 ventral portion; I.O. 4 , its communication with supra-orbital; I.O. 5 , canal communicates with 

 hyomandibular and bends inwards ; I.O. 6 , part of canal which dips into buccal groove ; I.O. 7 , union 

 of two infra-orbitals in front of mouth; I.O. 8 , union of two infra-orbitals at tip of snout; 

 t. 1 , t. 13 , t. 39 , t. &0 , tubules of canal; bu., buccal nerve with ganglion on its root, supplying infra- 

 orbital canal and inner and outer buccal groups of ampullae ; bu.o., branch for first part of canal — 

 this branch probably supplies the sub-orbital row of pit organs, p.o. 2 ; bu. 2 , outer division of buccal 



