304 ANATOMY OF THE CENTEAL NEEVOUS SYSTEM. 



seen by me in fetal brains and since more carefully studied by Westphal in 

 adult brains, lie in a dense net-work of nerve-fibers. It is not yet certain 

 whether these fibers are in connection with the motor-ocu.li nerve, and if so 

 how the connection is made. There is such an array of clinical observations 

 and of facts derived from post-mortem dissections that one may venture to 

 designate the portion of the nucleus from which the innervation of each 

 individual ocular muscle comes. I give here Starr's table, the latest of these 

 numerous attempts so happily begun by Pick. According to Starr, the 

 nuclei of the individual muscles are arranged from before backward thus: — 



Sphincter iridis. Musculus ciliaris. 



Levator palpebrse. Eeetus internus. 



Eectus superior. Eeetus inferior. 

 Obliquus inferior. 



PI . 



^ Pi 



The nerves for the intrinsic muscles of the eye arise probably from the 

 anterior nucleus. The crossed tract, possibly also the median portion of the 

 posterior nucleus, are to be accredited to the internal rectus. Clinical ob- 

 servations show that there must be a direct and a crossed connection be- 

 tween the motor-oculi nerve and the centers of the optic nerve, but the 

 anatomical basis for this has not yet been established. Net-works and 

 bundles of fibers through which the connection might take place are abun- 

 dant in this region. Hut up to the present time there has been on this point 

 neither a conclusive experiment nor a convincing clinical observation with 

 a subsequent post-mortem demonstration. 



The motor-oculi nucleus lies ventral to the aqueduct of Sylvius: 

 i.e., in the floor of the aqueduct. Later, as we proceed to study the teg- 

 mentum backward, we will meet in the region of this floor the nuclei of 

 nearly all the other cranial nerves. 



At the beginning of this chapter it was stated that fibers pass backward 

 from the posterior commissure. Toward a jDoint located mesially and ven- 

 trally from these filjcrs fine bundles converge, which arise in the interbrain 

 below the anterior nucleus of the oculo-motorius. The sectional area covered 

 by these bundles becomes j)rogressively greater from before backward. They 

 are reinforced by many fibers from the motor-oculi nucleus itself. We shall 

 meet the somewhat triangular cross-section of this fascicle, which is made 

 up of such varied constituents, in all the sections from the corpora quadri- 

 gemina down to the beginning of the spinal cord. It is called the posterior 

 longiiiirlinal fascicle {fasciculus loiuiitudinalis posterior). Since along the 

 whole course of this bundle fibers pass from it to the nuclei of the other 

 cranial nerves (readily seen in a fetus of six or seven months, where few 

 other fibers are medullated), and since its posterior end lies much beyond the 

 nucleus of the abducens it is probable that the posterior longitudinal fascicle 



