. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCII FISHES 227 brandies. The ])liarynu:eal is unlike tliat of the ninth only in that it first passes ))osteriorly and then cni-ves forward. The nerves posterior to the seventh cleft have undergone considerable cliange. The third division of the vagus, tlie ramus intestinalis (), breaks up into a numl)er of important divisions, some of which go to the lieart, others to the oesophagus, and still others to the stomach and associated parts. OCCIPITOSPINAL NERVES Arising ])osterior to the vagus are certain small nerves known as the occipi
. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCII FISHES 227 brandies. The ])liarynu:eal is unlike tliat of the ninth only in that it first passes ))osteriorly and then cni-ves forward. The nerves posterior to the seventh cleft have undergone considerable cliange. The third division of the vagus, tlie ramus intestinalis (), breaks up into a numl)er of important divisions, some of which go to the lieart, others to the oesophagus, and still others to the stomach and associated parts. OCCIPITOSPINAL NERVES Arising ])osterior to the vagus are certain small nerves known as the occipi tospinales (w-z, figs. 200a. 200b, and 204). These nerves are unusually numer ous in Heptanchiis and con- sist of both ventral and dorsal branches. The first pair to arise ventrally {w, fig. 200b) is near the mid- ventral line and not unlike the sixth or abducens nerve in origin. Posterior to this are three others (.r, y, z), making in all four ventral pairs. Dorsally in Heptan- chiis maculatus (fig. 200a) there are two pairs, the first of which joins the "(/" divi- sion of the ventral nerve. These nerves supply the subspinalis and dorsal interarcuales muscles (fig 204) and are like the spinal nerves with which .r, ;/, and z form a Fig. 204. Cervical and brachial plexus, IJcptancJtiis cinereus. (From Max Fiirbringer.) , brachial plexus; , cervical plexus; , dor- sal or sensory nerve; ^.,dorsal root ganglion; sp.,spinal (mixed) nerve; , ventral or motor nerve; «', x, y, s, occipitospinal nerves. SPIXAL NERVES A spinal nerve arising from the spinal cord in Heptanchus cinereus (M. Fiirbringer, 1897) is composed of a single ventral (motor) and a dorsal (sensory) root. The ventral root comes from cells in the ventral horn of the cord* {, fig. 201) and passes outward to be joined by the dorsal root (fig. 204); while the dorsal root extends to the dorsal horn of the cord (<:/./(., fig. 201) through the dorsal root ganglion (g., fig. 204).
Size: 2104px × 1187px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherberkeleycalifuniversityofcaliforn
