OCR Text |
Show 290 • ME. W. E. COLLINGE ON THE [Apr. 2, The Facial Group.-The only branch of the facial which I have been able to satisfy myself actually innervates a portion of the sensory canal system is the most posterior division of this group- the ramus hyoideus-which runs in the ventral portion of the preoperculum and innervates the canal which traverses that bone. The ramus mandibularis (PI. X X . figs. 10, 11, r.m.) lies below the mandibular branch of the trigeminal and does not enter into relation with the branch of the canal. A small branch (PI. X X . figs. 10, 11, x) in some cases was in very close relationship with the sub-orbital branch of the main canal, but no fibres could be traced to the sensory organs. There would seem to be no innervation to the upper portion of the canal in the preoperculum, neither the ramus oticus nor the glossopharyngeal entering that region. The Vagus passes directly backwards, giving off a lateral branch and other smaller branches. Tbe lateralis vagi lies dorsally as far back as the supraclavicle, passing beneath that bone, at a point about at its upper third ; it then makes a downward curve to the region of the lateral canal, which it innervates. V. SALMONID.E. SALMO SALAE. General Description. The lateral canal commences at the base of the caudal fin and passes anteriorly as a dermal canal. In its course forwards it opens to the surface by a series of pores which pass between the scales, those scales in the region of the lateral canal being slightly modified. It enters upon the head in the region of the pterotic bone, giving off an occipital commissure and, anterior to this, the operculo-mandibular branch. Posterior to tbe orbit it divides into supra-and sub-orbital branches, the former passing some little distance above the orbit and the latter through a series of canal-bones forming the circumorbital ring. A number of variations in the branching and distribution of the main canal of tbe head and its branches were noted in the various specimens dissected. I shall first describe what I consider to be the typical form, and then make mention of some of the variations met with. Course of the Canals and Branches. 1. The L A T E E A L C A N A L is a dermal one like that in Esox; it commences at the base of the caudal fin, and in its course forwards opens to the surface by a series of pores which, as described above, pass between the scales, there being a slight modification in those scales in the region of the lateral canal. 2. The M A I N C A N A L of the head is a fine canal enclosed within a series of small drainpipe-like canal-bones (PI. X X . fig. 15), not unlike those figured and described in Polyodon (3. pi. 39. fig. 7,e). It enters upon the region of the head above the pterotic and gives off an occipital commissure in the occipital |