1 66 Journal of Comparative Neurology. 



histology. 



Oblongata. — The account of this important portion of the 

 brain is very incomplete, from the lack of time and suitable 

 material, as well as the natural complexity of its structure. In 

 the adult the cells can be made to take the silver impregnation 

 only with great difficulty, and the unavailability of fresh larval 

 material has rendered very unsatisfactory the study of their re- 

 lations. The form of the cells of the myel and oblongata in Am- 

 phibia has been shown by Fish and others. The cells of the dorsal 

 and lateral regions are pear-shaped, the simple process extend- 

 ing toward the periphery and branching profusely. The motor 

 or ganglion cells in the ventral and lateral regions are multipolar 

 or fusiform and their processes extend peripherally into the alba 

 and are greatly branched. 



The transition from the myel to the oblongata is a gradual 

 one ; even as far caudad as the second spinal nerve, the typical 

 structure of the myel is somewhat modified. A transection of 

 the cervical myel is shown in Fig. 9. In accordance with the 

 conditions in higher forms, the alba may be divided, more con- 

 veniently than naturally perhaps, into dorsal, lateral and ventral 

 columns. The compressed myelocoele is bordered by two or 

 three layers of endymal cells. The dorsal and ventral cornua 

 of the cinerea are present, but are weakly developed. The 

 dorsal send projections ectad, interrupting and dividing into 

 small bundles the longitudinal fibers of the alba. The cells in 

 the myel are mostly small, their processes directed peripherally. 

 In the ventral horns are the characteristic large cells, which also 

 occur in the lateral region. Occasional fusiform cells were like- 

 wise observed which sent their processes into the raphe. The 

 fibers of the ventral columns are mostly coarse, especially those 

 immediately ventrad of the cinerea, the posterior longitudinal 

 fasciculus and the Mullerian fibers of Osborn^ with which are 

 associated the larg-e Mauthner fibers. 



1 Osborn is not quite clear in the terms in which he speaks of the fibers of 

 this region. The fibers immediately ventrad of the cinerea on each side of the 

 meson, he called the posterior longitudinal fasciculus ; those farther ventrad, 

 Mullerian fibers, presumably from a supposed homology with the fibers of that 



