Anatomy of the Brain of Bdellostoma Dombeyi 13 



does mean. Max Fiirbringer, '97, calls the lateralis posterior the first 

 spino-occipital nerve. Holm, '01, who has done very good work on the 

 internal structure of the brain of Myxine, and who has produced some 

 beautiful plates, unfortunately follows Sanders in this matter, as in 

 several others of equal importance, and considers the second trunk of 

 the trigeminus to be composed entirely of general cutaneous fibers, 

 though he recognizes that its root is distinct from the rest of that 

 nerve. The lateralis posterior he has apparently failed to find. None 

 of these writers, even those who have dealt with the internal anatomy 

 of the brain, have shown a true conception of the complex nature of 

 these trigeminus trunks; Allis, '03, comes nearest, when he calls the 

 second trigeminus trunk r. huccalis lateralis n. trigeminus II. He has 

 not found the larger trigeminus component of this trunk, but considers 

 it to be solely lateralis in character, and declares it to be homologous 

 with the huccalis facialis of the higher fishes. In addition to this, Allis 

 finds lateralis fibers in the first trunk of the trigeminus, and finds also 

 the lateralis posterior, which he interprets correctly as a lateral nerve, 

 and, while not feeling sure of its homology, is inclined to call it the 

 linecv lateralis vagi. 



Summary. 



We find that the several parts of the acusticus nucleus are connected 

 with each other by individual cells and their processes. The acusticum 

 is connected with its fellow of the opposite side of the brain and with the 

 general cutaneous nucleus of its own side by individual cells. The 

 connections between the acusticus and general cutaneous nuclei are both 

 numerous and intimate, as shown by the very considerable number of 

 cells lying on either side of the boundary that send out interpenetrating 

 fibers between the two. This close connection tends to support John- 

 son's theory that the tuherculum acusticum and the general cutaneous 

 nucleus have developed concomitantly from the same fundamental part, 

 the dorsal horn of the spinal cord, — the morphological differentiation 

 being due to a division of labor with a specialization of function. 

 Certain cells of the acusticus nucleus send fibers into the tractus fasci- 

 culus communis just as they do into the general cutaneous nucleus. 

 Whether this is reciprocated by the cells of the communis nucleus has 

 not yet been ascertained. The acusticus nucleus is connected with the 

 lobe of the cerebellum of its own side of the brain by individual fibers. 



