108 
veins (V. hep.) which enter the lower portion of the sinus 
venosus on its posterior side. 
E.—THE NERVOUS SYSTEM. 
We shall commence our description of the nervous 
system with the brain and spinal cord, then proceeding to 
the cranial and spinal nerves, and finally to the 
sympathetic nervous system. 
1.—TuHer Bratn anp Spinat Corp.* 
(Figs. 28, 30, 51). 
The brain of the Plaice may be conventionally 
divided into four regions, including the following 
structures : — 
A. Hind- Brain —This comprises the medulla 
oblongata, which itself includes many structures that can 
only be regarded as the continuations of corresponding 
ones in the spinal cord, and the cerebellum. The latter 
consists of a body and the anterior valvula cerebell. 
B. Mid-Brain. —Formed by a base (crura cerebri) and 
side wall, and the tectum opticum or tectum mesencephali 
(optic lobes). 
C. IT ween-Brain.—Represented by three parts: (1) 
the epithalamus (epiphysis generally and the ganglia 
habenule); (2) the thalamus (optic thalami—thalamence- 
phalon); (3) the hypothalamus (corpus geniculatum, 
* The following works will be found to contain references either to the 
brain of the Plaice or to allied Pleuronectids :—Cattie, Arch. Biol., iii., 
p. 150; le Roux, ‘‘ Recherch. Syst. Nerveux Téleostéens,’’ Caen, 1887 
Mayne, ‘‘ Optic Nerves,” Todd’s Cyclopedia, part xxvi.; Malme, Bihang 
K. Svens. vet.-akad Handlingar, xvii.; Mayer, Verhand. K. Leop.-Carol., 
xxx.; and Steiner, ‘‘ Entstehung d. asymmetrischen Baues der Pleuronec- 
tiden,” 1886; a recent important work, by J. B. Johnston, on the brain of 
Acipenser (Zool. Jahrb., Abth. Morph., xv.), may be used as a starting 
point in studying the brain of Fishes in detail. 
