72 PROFESSOR J. C. EWART ON THE 



the hyomandibular corresponds to the angular and jugular canals [ang. and j., fig. A) of 

 Garman. It lies immediately under the skin, and gradually diminishes in size from 

 before backwards. It receives eighteen branches from the hyomandibular nerve, and 

 communicates with the surface by eighteen tubules and a small terminal pore. The 

 majority of the tubules run directly outwards, and are consequently extremely short ; 

 but a few which run obliquely inwards are slightly longer. 



As already mentioned, the hyomandibular (operculo-mandibular) is more extensive in 

 Amia than in Lsemargus. Beginning on a level with the infra-orbital canal (HM. 1 , 

 fig. 3), it courses downwards and forwards to reach and extend along the entire length 

 of the mandible (HM. 2 , fig. 3). In the case of Chlamydoselachus, the lower or mandi- 

 bular portion (oral of Garman) is complete ; and there are, in addition, to use Garman's 

 terms, angular (ang.), jugular (j.), spiracular (sp.), and gular (g.) portions (fig. 4). 



In some sharks, the mandibulars are represented by a continuous commissural canal, 

 in others by two short isolated canals ; but in the skate, as will be described in a future 

 paper, each hyomandibular gives off a long ventral loop, the outer limb of which reaches 

 the dorsal surface, and runs backwards to terminate in an offshoot from the lateral 

 canal. 



Innervation of the Hyomandibular Canal. — The sense organs of the hyomandibular 

 canal in Lsemargus are supplied by branches of the hyomandibular nerve, which leave the 

 main trunk in the region of the hyoid group of ampullae. 



4. The Canal of the Lateral Line. — This canal may be said to consist of three 

 portions : — (1) the trunk portion, which, beginning on a level with the spiracle, extends 

 backwards along the side of the body to end on a level with the terminal portion of the 

 vertebral column; (2) a transverse portion (lc., fig. 1), which runs inwards behind the 

 auditory pore to form with a corresponding portion from the canal of the opposite side 

 the temporal commissure ; and (3) a short pre-oommissural part (lp., fig. 1) which 

 runs forwards to join the otie portion of the infra-orbital. All the three parts (with the 

 possible exception of the portion immediately behind the otic) are supplied by the nervus 

 lateralis. The anterior or pre-commissural portion measured 1*25 cm. in length. It 

 receives branches from the most anterior fibres of the lateralis nerve, and opens to the 

 exterior by five tubules which curve outwards and backwards. This portion of the lateral 

 corresponds to a part of the occipital canal of Garman (oc., fig. A). Further investiga- 

 tions may show that one or more of its sense organs are, as in Amia, supplied by the 

 glossopharyngeal nerve. The commissure (aural canals of Garman, au., fig. B) connect- 

 ing the two main lateral canals was 8 cm. in length. Eunning across from 3 to 4 mm. 

 beneath the surface and about 6 mm. behind the auditory pores, it opens through the 

 skin by sixteen short, delicate tubules, and its floor is perforated by sixteen pores for 

 branches of the most anterior fasciculus of the lateralis nerve. It may be mentioned that 

 in Chlamydoselachus, the temporal commissure lies in front of the auditory pores and 

 has no tubules (fig. 5). This difference in the relation of the canal to the auditory pores 

 is more apparent than real ; for even in Chlamydoselachus the commissure lies behind 



