OCR Text |
Show 880 MR. W. WOODLAND ON THE [Nov. 27, of the superior maxillary and the small size of the mandibular may perhaps be correlated with the general conformation of the skull- the elongated snout, probably used in " grazing" along the sea-bottom, rendering the movements of the lower jaw of little importance. In the dissection of the right orbit there is clearly observable a large ganglionic mass (G) in connection with the second and third roots of the fifth and seventh, and from this there arise numerous small nerves supplying the muscles in front of the spiracle and elsewhere. From the most posterior root of the three by which the fifth and seventh nerves originate, there early arises the most characteristic division of the facial nerve, viz. that which bifurcates over the spiracular cleft. The prespiracular branch is small but obvious; the postspiracular is large, and just below the spiracle divides as usual into the internal mandibular branch (chorda tympani), which, as shown in fig. 17 (PI. L X I .), extends a long distance anteriorly under the orbit, and the external mandibular. According to the above provisional identification of the various branches of the trigeminal and facialis, fibres of the seventh nerve occur in both the anterior and posterior of the three roots. The disposition of the occipito-spinal nerves of C. calceus is represented in fig. 14 (PI. L X .). As shown, two nerves originate, ventrally to the vagus, in front of the spinal nerve corresponding to the first vertebra (the first spinal). This statement is contrary to that of Fiirbringer10, who provides figures of a longitudinal section of the hind part of the skull of C. calceus in which four such occipital nerves are shown, and of the occipito-spinal nerves of C. granulosus in which the presence of four is also implied. My dissection of these nerves was from the ventral surface and was carefully made ; I could not, however, observe more than two occipito-spinal nerves, as shown. These join with the first two spinal nerves to form a single trunk which afterwards divides into twTo branches, one forming a constituent of the brachial plexus, and the other supplying the muscles of the lower jaw. Spinal nerves 3-1 2 share in the formation of the brachial plexus. The vagus has, in addition to the branchial, visceral and lateral-line branches, two small ones, arising respectively from the main trunk (just in front of and dorsal to the visceral) and from the lateral-line branch near its origin, which run to dorsal muscles more or less parallel with the vertebral column. I did not determine the exact number of spinal nerves forming the pelvic plexus, but I may state that I counted seven. R em arks on th e S k e l e to n . Gegenbaur has supplied a full account of the head-skeleton of ( \ calceus in the work before referred t o s, and I have very little to add to his account. In the lateral view of the skull provided by Gegenbaur (Taf. xii.), the extremely large, slightly-curved process situated anteriorly on the upper edge of the upper jaw is not at |