NERVUS TERMINALIS : MAMMALS 63 



.tionship with the special visceral afferent group. As previously 

 noted, Brookover states that the origin of the nervus terminaUs 

 in the ganoid fishes studied by him is from a portion of the ol- 

 factory placode. Locy, in describing its early development in 

 Squalus, attributes its origin to the neural crest, but states also 

 that "The new nerve has at first a fusion (placode) with the 

 thickened surface epithelium, located just above the shallow de- 

 pression that marks the beginning of the olfactory pit. This 

 connection between the surface epithelium and brain- wall, con- 

 sists of a group of closely packed cells in which I have failed at 

 this early stage [6 to 8 mm.] to recognize fibers." If this pla- 

 code described by Locy be homologous with that found by 

 Brookover, the embryonic evidence in the two groups on which 

 these writers worked points to an origin which in part at least 

 corresponds to that of other special sensory ganglia in the head 

 region. 



In connection with the free nerve terminations described, this 

 embryonic origin of the nerve from a placode suggests the conclu- 

 sion that there is a sensory component of the terminalis which is 

 distinct from the sensory fibers which terminate in the walls of 

 the blood-vessels. The neuroblasts which have their origin in 

 the neural crest might well give rise to the sympathetic cells 

 described and figured in the present article, and which have 

 been described in other groups of vertebrates than the mammals 

 in the nerve under consideration. The free nerve terminations 

 in the mucosa do not, however, seem to fit in with the view that 

 this sensory component belongs to the special visceral system. 



5. Many physiologists find insufficient evidence of vasomotor 

 control of the cerebral blood-vessels. Wiggers ('05, '08) and 

 Weber ('08) have presented experimental support of the histo- 

 logical evidence. Both conclude that there is direct physiological 

 proof of nerve control over the cerebral vessels. Weber, more- 

 over, finds indications that there is an accessory vasomotor 

 center further rostrad in the brain than that situated in the bulb. 



This observation is suggestive, in connection with McKibben's 

 findings in urodeles, of terminalis tracts extending to the inter- 

 peduncular region, with a probable center in the neighborhood 

 of the preoptic nucleus. 



