EXPLANATION OF THE PLATES. 



PLATE L 



IN Figs. 1 to 9 inclusive, corresponding parts are indicated by the same letters. 



Olfactory Lobes A. 



Cerebral Lobes B. 



Corpora Striata C. 



Optic Thalami D. 



Pineal Body E. 



Pituitary Body F. 



Optic Lobes G. 



Cerebellum H. 



FIG 1. Cerebro-spinal axis seen from beneath, enlarged four times, linear measurement, showing the 

 origins of the cranial and spinal nerves. 



I. Olfactory nerve ; II. Optic nerve ; III. Motor communis ; IV. Patheticus ; V. Trigeminus. 



a, portio dura, or facial, which joins the ganglion of the trigeminus ; J, motor externus or abducens, 

 which also joins the ganglion of the trigeminus; c, " facial," a nerve formed by the union of a branch 

 from the trigeminus with another, d, from the vagus. 



VI. Auditory nerve. 



VII. Vagus, d, branch joining the " facial " ; e, motor root ; /, cutaneous branch ; g, h, glosso-pha- 

 ryngeal. 



I. First enlargement, or medulla oblongata. 



L. Brachial enlargement. 



N. Lumbar, or crural enlargement. 



0. Coccygeal portion. 



1, i. Crystal capsules connected with all of the spinal nerves, except the tenth pair. 

 k, k. Ganglia of the spinal nerves. 



FIG. 2. Dorsal view of the cerebro-spinal axis, enlarged two diameters, linear measurement. A, B, D, 

 E, G, H, the same as in Fig. 1. K, fourth ventricle. L, posterior pyramidal tract, enlarged at each 

 of the bulgings of the chord ; the posterior pyramids form a similar enlargement for the medulla oblon- 

 gata, but are separated by the fourth ventricle. 



FIG. 3. Side view of the cerebro-spinal axis. Letters indicate the same parts as in the preceding 

 figures. 



FIG. 4. Brain and spinal chord of Bufo Americanus. References as before. 



FIG. 5. Brain of Menolrranchus lateraUs. The optiolobes, G, are fused, as in Menopoma, and as are 

 the olfactory lobes in Frogs and the cerebral lobes in some Plagiostome Fishes. 



FIG. 6. Transverse section of the brain, showing the cavities of the olfactory, cerebral, and optic lobes. 



