ELASMOBRANCH BRAIN ORGANIZATION 



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1 mm 



Figure 2 Transverse sections through the diencephalon and mesencephalon of Squalus 

 acanthias. In this figure and Figures 3-5, a photograph of a Nissl preparation is shown on 

 the right. To the left is a drawing of the contralateral brain wall charting the course of the 

 retinal projections. Fibers of passage are indicated by dashed lines, and terminal fields by 

 stippling. (A) rostral thalamus, (B) midthalamic level and rostral pole of tectum, (C, D) 

 caudal thalamic levels. C, central tectal zone; CP, central pretectal nucleus; DT, dorsal 

 thalamus; FB, forebrain bundles; FR, fasciculus retroflexus; H, habenular nuclei; HC, 

 habenular commissure; HY, hypothalamus; IL, inferior lobe of hypothalamus; NP, nu- 

 cleus profundus mesencephali; OC, optic chiasm; ON, optic nerve; OT, optic tectum; P, 

 periventricular tectal zone; PA, preoptic area; PC, posterior commissure; PP, periven- 

 tricular pretectal nucleus; S, superficial tectal zone; SC, subcommissural organ; SP, super- 

 ficial pretectal nucleus; VT, ventral thalamus. 



