Anatomy of Mystus seenghala IV Nervous system

Uberoi, I. B. S.

The brain of Mystus seenghala has 3 parts, viz. the fore-brain or prosencephalon including the cerebrum, the olfactory lobes and the diencephalon; the mid-brain or mesencephalon constituted by the optic lobes alone; and the hind-brain or rhombencephalon consisting of the cerebellum and the medulla oblongata. The cerebrum is an undivided oval structure. The olfactory lobes are wedge-shaped thickenings along the inner ventral surface of the cerebrum and are anteriorly produced into the olfactory nerve. The diencephalon or the thalamencephalon is a band-like structure lying between the cerebrum and the mid-brain. From its dorsal surface arises a pineal stalk from the habenular ganglion. This pineal stalk bears a pineal body at its distal end. The infundibulum which lies below the diencephalon, bears a rounded hypophysis or the pituitary body distally. Posterior to the infundibulum are present a pair of bean-shaped lobi inferiores, behind which in the region of the mid-brain lies a small and transparent sac, the saccus vasculosus. The 2 optic lobes are partly covered and pushed apart due to forward prolongation of the cerebellum. The crura cerebri are not very well developed. The optic nerves though cross each other below the cerebrum yet there is no true chiasma. There are 10 pairs of cranial nerves, namely Olfactory, Optic, Oculomotor, Trochlear, Abducens, Trigeminal, Facialis, Auditory, Gloss opharyngeal and Vagus. A typcial spinal nerve arises from the spinal cord by a dorsal root coming out of a foramen present in the neural arch, and a ventral root which comes out of a foramen present either at the base of the neural arch or on the dorsolateral surface of the centrum. Befoee the union of the 2, the dorsal root gives off a branch called the ramus dorsalis which supply the dorsal fin. The sympathetic nervous system consists of a long and slender ganglionated cord lying on either side of the dorsal aorta. Each cord arises from a ganglion which is connected to the hyomandibularis of the facialis by nerve fibers.