PARIETAL AND PINEAL NERVES 



405 



habenular ganglion, the right bundle of Meynert, the ependymal groove 

 or " subcommissural organ," and, he believed, also in the posterior 

 commissure (Fig. 134, Chap. 17, p. 188). He likewise traced the con- 

 nections of the nerve-fibres issuing from the parapineal organ (anterior 

 or left pineal eye) to the left habenular ganglion, habenular tract, or 

 superior commissure, and the left bundle of Meynert, which is much 

 smaller than the corresponding bundle of the opposite side, which receives 

 the larger pineal nerve coming from the more highly evolved right pineal 

 eye. In his concluding remarks he states that " the connection of each 

 of the two sense-organs with the corresponding member of the habenular 

 ganglion-pair need no longer be questioned " ; and, further, " the 



Fig. 273.- 



-Section through the Vestigial Eye of a Frog Tadpole. 

 (After Dendy.) (From a photograph). 



168. 



ep. : epidermis. 

 p.e. : pineal eye. 



?-.s. : roof of skull. 



v.n. : vestigial stalk and nerve. 



marked asymmetry in point of size of the two habenular ganglia and of 

 the two bundles of Meynert corresponds exactly to the unequal develop- 

 ment of the two parietal sense-organs with which they are connected, and 

 leaves no doubt as to the paired character of the whole system." 



Without entering further into this highly controversial question, we 

 may conclude that these observations are highly suggestive of a system 

 of nerve tracts with commissures passing from the parietal sense-organs 

 to receptive centres in the brain, which in some respects is comparable 

 to that of the paired lateral eyes — in other words, a system of afferent 

 fibres of a sensory nature ; but, as might be expected from the vestigial 

 condition of the receptive organs in these animals, the fibres are usually 

 unmyelinated. 



