Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 NEKVOUS SYSTEM OF MOLLUSCA. 315 extending over the oesophagus, passes along the sides of the body in- ternally to the branch ias, and forms the pallia! nerve-trunk (pi). There is also a group of four small ganglia below the oesophagus (sublingual ganglia). The two trunks of the pedal nerves are thicker than the commissures which pass to them from the nervous baud; they must consequently be regarded as central parts of the system. They seem to be the longitudinal trunks of a 'ventral medull
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 NEKVOUS SYSTEM OF MOLLUSCA. 315 extending over the oesophagus, passes along the sides of the body in- ternally to the branch ias, and forms the pallia! nerve-trunk (pi). There is also a group of four small ganglia below the oesophagus (sublingual ganglia). The two trunks of the pedal nerves are thicker than the commissures which pass to them from the nervous baud; they must consequently be regarded as central parts of the system. They seem to be the longitudinal trunks of a 'ventral medulla/' in which the ganglionic cells are not definitely distributed into distiuct groups any more than they are in the Gephyrea. The structure of this chord re- quires, however, to be further investigated. The principal point in the arrangement of the nervous system in the Placophora is that we may recognise in it just the same relation of parts as in the Solenogastres, and specially in Chaetoderma (§ 121). § 207. The relatively feeble development of the cerebral ganglia in the Lamellibranchiata is due to the absence of a head, and its related sensory organs. These ganglia (Fig. 181, a) are often placed so much to the side that there is a long commissure be- tween them (Lucina, Pano- pasa, Anodonta, Unio, Mytilus, Area, Cardium, Pholas, etc.). A few smaller branches only are given off in addition to the large vis- ceral commissures. There are two pedal ganglia in- stead of the pedal nerve- trunks, the nerves from which are distributed in the ventral portion of the body, and especially in the foot. They are placed at the root of the foot, and are some- times deeply imbedded in it. The commissural chords vary in length in propor- tion to the development of the foot, and the distance between it and the anterior parts of the body. When the foot is feebly developed, or when it is produced very Ear forwards, the cerebral and pedal ganglia may be markedly approximated (Solon, Mactra).
Size: 1383px × 1446px
Photo credit: © Bookworm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
