NERVOUS SYSTEM. VERTEBRATA. 89 



specially strong. The tectum opticum has also essentially the 

 same structure in both groups, although its elements are in 

 Teleostea arranged somewhat more definitely in layers. The 

 ependyma and nervous tissue also are greatly developed on 

 either side o the mid-dorsal line of the tectum forming a pair of 

 longitudinal ridges (tori longitudinales), traces of which are also 

 found in Reptiles and Birds. The lateral parts of the optic 

 lobes contain a pair of large nuclei (n. laterales), from which 

 a considerable proportion of the fillet a particularly well- 

 developed tract in Teleosts takes its origin. They are super- 

 ficially visible as a pair of bulgings into the cavity of the optic 

 lobes (tori semicirculares) . The cerebellum and valvula show 

 the structure common to the cerebellum of all Vertebrates ; 

 PurkinjVs cells are, however, somewhat irregularly disposed. 

 The valvula is connected by tracts to the lobi inferiores. 



ANACANTHINI. 



D. 87. The cranium of a Cod ( Gadus niorrhua) in sagittal section, 

 showing the brain from the left side. The cranial cavity is 

 very extensive, and is only partially occupied by the relatively 

 small brain. The latter shows well the main Teleostean 

 characters. The olfactory bulbs are small round bodies 

 lying close beneath the olfactory capsules; they are con- 

 nected by long delicate tubular peduncles (the ventral parts 

 of which only are nervous) to the basal region of the cere- 

 brum. The peduncles lie close side by side for the posterior 

 two-thirds of their course ; in front they diverge towards 

 the olfactory capsules and gradually increase in calibre. 

 The basal ganglia of the cerebrum form two pronounced 

 swellings of the cerebral floor; they are separated from 

 one another dorsally by a deep sagittal fissure and are 

 ventrally united by a transverse commissure. Each is dis- 

 tinctly tabulated, the two main lobules (striatum and 

 epistriatum) lying respectively antero-lateral and postero- 

 mesial. The roof of the cerebrum (pallium) is entirely 

 non-nervous and consists of a continuation of the ependyma 

 that lines the brain-cavities, in conjunction with the pia 

 mater. In front it is continuous with the epithelial roof 

 of the olfactory tracts, and behind with that of the thalamen- 



