9 2 



NATURE 



{May 24, 1888 



heat is increased by reversing or even simply interrupting the 

 current, which is in accordance with the modern theories on 

 thermodynamics and molecular polarization. But all these ex 

 periments are merely preliminary studies in a field of vast and 

 increasing importance, the cultivation of which may ultimately 

 lead to the greatest discovery of modern times, the deter- 

 mination and application of the laws by which the material 

 universe is governed even in phenomena of a psychic order. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, March 8. — "Contributions to the Anatomy 

 of the Central Nervous System of Vertebrate Animals : 

 Anatomy of the Brain of Ceratodus forsteri" By Alfred 

 Sanders, M.R.C.S., F.L.S. 



The brain of Ceratodus has the following general arrangement : 

 the membrane which represents the pia mater is of great thick- 

 ness and toughness ; there are two regions where a tela choroidea 

 is developed ; 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 thalamencephalon and the mesencephalon are narrow, 

 and the medulla oblongata is wide. The ventricles are all of 

 large size, and the walls of the lateral ventricles are not com- 

 pleted by nervous tissue. All the cranial nerves are to be seen 

 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 off-shoot from the ramus lateralis ; the ganglion 

 gives off the branchial nerves and the ramus intestinalis, the 

 ramus lateralis passing on without entering it. 



The minute structure of the dorsal part of the cerebrum 

 presents four layers : externally a layer of finely granular 

 neuroglia, with slight indications of radial striation ; next a 

 layer of larger-sized cells ; then another layer of neuroglia, 

 with fibrillar having a tendency to a longitudinal direction ; and 

 internally a layer of rounded cells closely crowded together. 

 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 olfactori, which seem as if 

 they were the external layer of the cerebrum condensed ; and 

 between the two, 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 fibrillae which collect into a commissure in the central 

 line at the dorsal surface. This layer also contains fusiform 

 and rounded cells sparsely scattered through it ; and inter- 

 nally there is a layer of cells mostly rounded. At the central 

 line on the dorsal surface there is a ganglion of large cells 

 resembling those of the optic lobe of the Plagiostomata. 



The cerebellum is a mere bridge over the fourth ventricle. 

 Its structure presents the usual number of layers : internally the 

 fibrous layer, which ultimately forms the crura cerebelli ad 

 medullam ; then the granular layer, the cells of which are of 

 large size compared to those of the same layer in Teleostei and 

 Plagiostomata ; then a layer of Purkinje cells, of which the form 

 and the number of processes are not uniform ; externally is the 

 molecular layer, which consists of a coarsely granular network 

 derived from the processes of the Purkinje cells, also a network 

 of finer fibrils and many rounded cells. 



In the spinal cord there are three columns of longitudinal fibres 

 on each side in the white substance : viz. the ventral columns 

 between the two ventral roots of the spinal nerves ; the lateral 

 columns between the dorsal and ventral roots ; and the dorsal 

 columns between the two dorsal roots. Fibres of large size are 

 scattered throughout the two former columns, but collected 

 principally in the ventral. The dorsal consists entirely of minute 

 fibres. 



The principal feature in the white substance is a fibre of gigantic 

 size, which is situated on tl e summit of the ventral columns, one 

 on each side; it consists of a common medullary sheath ; inclosing 



(where the fibre is largest) about 40 to 50 axis-cylinders ; these 

 have the character of the axis-cylinders of the ordinary fibres of 

 the white substance, but have no separate medullary sheaths ; 

 this fibre is traceable throughout the spinal cord ; commencing 

 opposite the posterior end of the abdomen, it extends to a short 

 distance behind the exit of the facial nerve ; it varies in size, 

 and becomes of the greatest diameter near the posterior end of 

 the medulla oblongata ; its axes escape through the medullary 

 sheath, and join the longitudinal fibres of the ventral columns. 

 Near its anterior termination all the axes have escaped except 

 one ; at this point it bears a great resemblance to Mauthner's fibre 

 in the Teleostei. This remaining fibre decussates with that of 

 the other side a short distance behind the exit of the facial nerve, 

 and enters the root of that nerve on the opposite side. 



In the gray substance of the spinal cord, there are two series 

 of ganglia, one in the ventral horn, which consists of multipolar 

 cells often of very large size. They send processes into the ventral 

 and lateral columns, which often become the smaller-sized longi- 

 tudinal fibres. The cells of the other series of ganglia are of 

 smaller size, and are situated in the substantia gelatinosa cen- 

 tralis ; they are smooth in outline, and give off one or two pro- 

 cesses ; they probably have to do with the dorsal roots of the 

 spinal nerves. Cells also of this kind occur at other places, as 

 in the fibr?e rectse, and in the field of the ventral columns. 



The transverse commissures are : one in the spinal cord, which 

 passes through the substantia gelatinosa centralis over the central 

 canal ; another on the ventral side of the anterior part of the 

 medulla oblongata, which corresponds to the commissura ansu- 

 lata of the Teleostei, and is connected with the commissure in 

 the dorsal part of the optic lobes ; then there is the posterior 

 commissure at the posterior part of the third ventricle ; and a 

 commissure at the posterior end of the cerebrum which is the 

 anterior commissure. 



There is no chiasma of the optic nerves visible externally ; what 

 there is of it, is situated in the substance of the thalamencephalon. 

 The anterior root of the fifth nerve arises from a ganglion 

 occupying a broad swelling at the lateral part of the gray matter 

 of the floor of the fourth ventricle. The posterior root arises 

 from the summit of the restiform bodies. 



The facial passes backward in a small tubercle at the junction 

 of the floor of the fourth ventricle with the restiform bodies. 



The acusticus arises from a bundle of fibres which are situated 

 on the summit of the ventral column, and appear to be a con- 

 tinuation forward of part of the multi-axial fibre which has not 

 decussated. 



The five roots of the vagus pass backward, and enter in suc- 

 cession the same tubercle as, and to the outside of, the facial 

 nerve ; the three posterior roots are double, so that the vagus 

 is equivalent to eight nerves, and consists entirely of dorsal 

 roots. 



Two nerves are given from the ventral side of the medulla 

 oblongata, each of which has two roots ; they do not join the 

 vagus, and pass back some distance within the vertebral canal, 

 and emerge on a level with the exit of the dorsal roots of the 

 spinal nerves. 



The second and third spinal nerves supply the pectoral fin, 

 and follow the course usually pursued by the hypoglossal when 

 that nerve is present in Teleostei. 



The fibres of the ventral roots of the spinal nerves enter in a 

 direction upward and forward toward the inner edge of the multi- 

 axial fibre, between it and the central canal, and then passing 

 over the dorsal edge of the same are either lost in the gray sub- 

 stance of the ventral horn, join a process of one of the multi- 

 polar cells, or become one of the longitudinal fibres of the 

 ventral columns of the cord. 



The brain of Ceratodus presents an embryonic condition in 

 three points : viz. first, in the extreme size of the ventricles and 

 the tenuity of the substance of their walls ; second, in the alter- 

 nating origins of the dorsal and ventral roots ; third, in the origin 

 of the dorsal roots close to the central line. 



Compared to Protopterus, it differs in the shape and imper- 

 fection of the cerebral lobes, and in the fact of its having a well- 

 developed rhinencephalon ; but it agrees in the narrowness of 

 the mesencephalon, and breadth of the medulla oblongata, and 

 in the rudimentary character of the cerebellum. 



Ceratodus agrees also with the Ganoids in the comparative 

 narrowness of the mesencephalon, and in the proportions of the 

 cerebellum. 



With the Plagiostomata it agrees in the structure of the optic 



