104 J. B. JOHNSTON 



EMYS LUTARIA 



Two embryos of this turtle were studied in Dr. Huber's labo- 

 ratory. In embryo jP, 10 mm. in length, the nervus terminalis 

 arises from the rostral end of the medial wall of the hemisphere, 

 caudal to the olfactory bulb, descends over the medial surface of 

 the bulb and olfactory nerve and bears clumps of ganglion cells 

 at several points of its course (fig. 9). It comes into close rela- 

 tion with the dorsal division of the olfactory nerve but is dis- 

 tinguishable from it. 



The peripheral distribution of the nerve is clearer in the 20 mm. 

 embryo {K), in which it becomes more closely related to the 

 dorsal division of the olfactory nerve. As shown in figure 11, 

 the formatio olfactoria in the bulb is divided into dorsal and 

 ventral portions. The dorsal portion receives the dorsal division 

 of the olfactory nerve and the appearances in the bulb alone 

 strongly suggest comparison with the vomero-nasal nerve and the 

 accessory bulb into which it enters in marsupials and mammals. 

 When the dorsal division of the olfactory nerve is traced distally, 

 however, it is found to take a peculiar course which is illustrated 

 diagrammatically in figure 10. It remains distinct from the ven- 

 tral division, passes downward in the septum over the wall of 

 a medial diverticulum of the nasal sac, turns laterad beneath the 

 sac and is distributed to the wall of the most lateral portion of 

 the nasal sac, situated beneath the orbit. This course and dis- 

 tribution seems to preclude the possibility of comparing this dor- 

 sal division of the nerve with the vomero-nasal nerve of mammals. 

 The medial diverticulum of the nasal sac in this embryo seems 

 to be the beginning of the vomero-nasal organ, and this is inner- 

 vated by the ventral division of the olfactory nerve and in part 

 by the nervus terminalis (fig. 10). 



The nervus terminalis appears in sagittal sections rather far 

 dorsally in the medial wall of the hemisphere (fig. 12 A). It 

 passes forward over the medial wall of the bulb, converging with 

 its fellow until they touch where the tips of the olfactory bulbs 

 approach closest to the median plane (fig. 12 C). The nerve then 

 passes alongside the dorsal division of the olfactory nerve and 

 becomes somewhat mingled with it. At intervals groups of 



