336 HOWARD AYERS 



innervating the hypophysial organ. In Bdellostoma the hypo- 

 physial branches are given off from the terminal nerve. In 

 mammals it has been shown by Huber and Guild^ and LarselP 

 that both terminal and septal branches run to the organ of 

 Jacobson, i.e., the terminal organ. In Bdellostoma, the gan- 

 glion cells of the terminal nerve lie in the terminal organ (fig. 23). 



4. CHIMPANZEE AND MAN 



In man as described by Brookover^ and in the chimpanzee, as 

 my dissections disclose (fig. 24) the N. terminalis leaves the 

 brain ventrad and mesad of the olfactorius and passes forward 

 to the lamina cribrosa. In man they pass through this plate 

 along with the septal and olfactory nerves and run ventrad to 

 terminate in and about Jacobson's organ. In the chimpanzee 

 the nerve on leaving the brain enters the pia and takes its course 

 forward to near the lamina cribrosa where it passes into the 

 dura and leaves the cranial chamber along with the bundles of 

 olfactory fibers. Its course outside the cranial chamber was not 

 traced. The recently published researches of Larsell^ on sev- 

 eral mammals show conclusively that both the terminal and 

 septal nerves are, in this class, preserved in their original rela- 

 tions to the olfactory nerve and brain. The nasal chamber in 

 man, therefore, contains the surface distribution of these three 

 most ancient cranial nerves as well as the surface terminations of 

 invading branches of a fourth and more recent cranial nerve, the 

 trigeminus (fig. 25). 



5. THE ANTERIOR CRANIAL NERVES 



We thus find that the nasal septum and related parts form one 

 of the most ancient and least changed morphological complexes 

 in vertebrate anatomy. Reacting to physiological necessity, 

 the advanced outposts of the central nervous apparatus of verte- 

 brates were withdrawn early in the life of the phylum more or 

 less deeply into the protective hood furnished by the overgrowth 

 of the muscles supported by added skeletal structures, and body 

 covering from territory lying behind the region of the primitive 



