26 CHARLES R. ESSICK 



matrix of the original ventricular gray matter takes place in the 

 formation of the cerebral cortex. (3) Subsequent to a definite 

 bending in the medullary wall, newly formed gray masses may be 

 transferred from the dorsal to the ventral portion of the brain by 

 a migration of cells in a tangential direction, e.g., arcuate forma- 

 tions, olive and accessoiy olives, and a part of the nuclei lying in 

 the pons. The third of these processes as described by His is 

 responsible for the development of the gray matter constituting 

 the arcuate nuclei of the medulla and the basilar nuclei of the pons. 

 The compact manner in which the neuroblasts arrange them- 

 selves in their migration to the pontine flexure, has attracted the 

 attention of many observers both in macroscopic and microscopic 

 preparations, nevertheless, with the exception of Streeter ('12) 

 only a casual mention of it has been made by them. Blake ('00) 

 in his description of the roof of the fourth ventricle noted cells 

 which were transferred to the ectal surface of the oblongata by 

 the formation of the secondary rhombic lip and he could trace 

 them in many embryos as far cephalad as the trigeminal nerve. 

 He ventured the suggestion that they might be connected with the 

 ganglia of some of the cranial nerves. His ('04) has given a good 

 illustration (fig. 103) of the rhombencephalon of a 5 cm. fetus 

 and has shown the outlines of the thick mass of cells passing from 

 the rhombic lip to the pontine formation. From its appearance 

 with the naked eye, as well as in serial sections, he identifies it 

 with the Corpus Trapezoides, which thus occupies a superficial 

 position at this time (p. 163). Streeter ('07) in dissections of the 

 Seventh nerve in pig embryos called attention to the presence of a 

 ganglion mass connected with the pons ganglia which could be 

 traced backward as a surface ridge between the facial and acoustic 

 nerves, to end on the dorso-lateral surface of the restiform body. 

 Since then he has suggested ('1?) two possible origins for the 

 pontine nuclei : the corpus ponto-bulbare and the mantle zone of 

 the pontine region. Neuroblasts from the latter source emerge 

 through the marginal zone as happens with the cortical cells of 

 the cerebellum. Orzechowski ('08) in human foetus measuring 

 17 and 23 cm. has described ganglion masses connecting the 

 rhombic lip, lateral recess wall and pons, which he considers the 



