10 



Mr. A. Sanders. On the Anatomy of the [Jan. 7, 



III. "Contributions to the Anatomy of the Central Nervous 

 System of Plagiostomata." By Alfred Sanders, M.R.C.S., 

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

 December 11, 1885. 



(Abstract.) 



After referring to the literature of the subject, the author gives a 

 short account of the macroscopic appearance of the brains of the 

 following species of Plagiostomata, viz., Raja batis, Rhina squatina, 

 Scy Ilium catulus, and Acanthias vulgaris. He then refers to the 

 distribution of the cranial nerves, especially of the trifacial and 

 vagus, pointing out the resemblance of the distribution of the last- 

 mentioned nerve in Rhina to that described by Gegenbaur* in 

 Hexanthus ; the difference lying in the fact that in the former the 

 rami branchial es of this nerve, the number of which correspond to 

 the number of the branchial arches, divide into two terminal branches 

 only, the rami anteriores and posteriores, the third, the rami pharyngei, 

 being absent. 



On the other hand, in Scyllium the rami branchiales do not divide, 

 the terminal twigs, representing the rami pharyngei, only being 

 present. 



The lobi olfactorii consist of two parts, the lobe proper and the 

 peduncle. The lobe itself is more or less pear-shaped, broader at the 

 anterior end where it abuts on to the olfactory organ, and narrower 

 behind where it passes into the peduncle. It consists of three layers, 

 counting from before backward, or from outside inward. The posterior, 

 which is also the internal layer, occupies more than half of the lobe, 

 and consists entirely of a mass of small cells embedded in a network 

 of fibrillaD and granular neuroglia. This network is of extreme 

 tenuity, and the cells contained therein are oval, pear-shaped, or 

 spherical in shape, and contain a nucleus and nucleolus ; they give off 

 processes which join the network. In front of these, and outside to 

 a certain extent, is found a layer consisting of glomeruli olfactorii ; 

 these are elongated or pear-shaped masses arranged with their long 

 axes in the direction of the nerve fibres. They consist of a central 

 core of closely intertwined fibrillar ; externally the fibrils are of rather 

 larger size ; they run longitudinally in reference to the glomerulus ; 

 in their course elongated cells are developed. 



The anterior or external layer consists of interlacing bundles of 

 fibres which pass from the anterior ends of the glomeruli into the 

 olfactory organ. The bundles themselves are flat, but the fibrillse of 

 which they are composed are round. 



* " Jenaische Zeitschrif t," Bd. 6, 1871. 



