420 Mr. A. Sanders. Anatomy of the Central [Mar. 8, 



III. " Contributions to the Anatomy of the Central Nervous 

 System in Vertebrated Animals. Part I. — Ichthyopsida. 

 Section I. — Pisces. Subsection III. — Dipnoi. On the Brain 

 of the Ceratodus ForsterC By Alfred Sanders, M.R.C.S., 

 F.L.S. Communicated by Dr. Gunther, F.R.S. Received 

 February 23, 1888. 



(Abstract.) 



The brain of Ceratodus has the following general arrangement : 



The membrane which represents the pia mater is of great thickness 

 and toughness ; there are two regions where a tela choroidea is de- 

 veloped : one where it covers in the fourth ventricle, and the other 

 where it penetrates through the third ventricle and separates the 

 lateral ventricles from each other. 



The ventiicles are all of large size, and the walls of the lateral 

 ventricles are not completed by nervous tissue. The thalamence- 

 phalon and the mesencephalon are narrow, and the medulla oblongata 

 is wide. 



All the cranial nerves are present except the abducens and the 

 hypoglossal. There is a large communicating branch between the 

 trifacial and the vagus. The glossopharyngeal has no separate -root, 

 but is a branch of the vagus. The ganglion of the vagus is not the 

 termination of the main trunk, but is an offshoot from the ramus 

 lateralis ; the ganglion gives off: the branchial nerves and the ramus 

 intestinalis ; the ramus lateralis passing on without entering it. 



In the minute structure of the dorsal part of the cerebrum there 

 are four layers to be seen, externally a layer of finely granular neu- 

 roglia, with slight indications of radial striation ; next a layer of 

 larger sized cells ; then another layer of neuroglia with fibrillae having 

 a tendency to a longitudinal direction ; finally, a layer of rounded 

 cells closely crowded together on the internal surface. The ventral 

 part of the cerebrum has only two layers — the external of neuroglia 

 and the internal of rounded cells. 



The olfactory lobes resemble the cerebrum in structure ; there is an 

 internal layer of cells continuous with those of the cerebrum, and an 

 external layer of glomeruli olfactorii, which seem as if they were the 

 external layer of the cerebrum condensed ; between the two there is a 

 layer of longitudinal fibres on which fusiform cells are developed. 



The optic lobes also consist of four layers ; externally there is a 

 layer of longitudinal fibrils derived from the optic tract; then a layer 

 of smoothly granular neuroglia; then a layer of transverse fibrillas 

 which collect into a commissure in the central line at the dorsal 

 surface ; there are also fusiform and rounded cells sparingly scattered 



