338 WALTER E. DANDY 



NERVES OF THE PARS INTERMEDIA 



Only by dissection of the hypophysis can the nerve supply of 

 the pars intermedia be traced. By gently separating and retract- 

 ing the posterior lobe from the clasping mitten-like anterior lobe, 

 it is often possible to trace a single nerve fiber with its branches 

 passing down the stalk and spreading out over the pars inter- 

 media which envelops the posterior lobe (fig. 3). 



NERVES OF THE POSTERIOR LOBE 



It has been shown that the posterior lobe is supphed by a 

 median artery which is formed by the confluence of two branches, 

 one from each carotid artery immediately after its entrance into 

 the cavernous sinus. In the canine this vessel enters the pos- 

 terior lobe at the only point of dural attachment. Vital nerve 

 staining is somewhat more difficult in this region on account of 

 the relatively thicker dural covering which excludes the action 

 of the air and necessitates a delicate dissection of this vessel. 

 For a long time we were unable to find any trace of a nerve 

 entering the posterior lobe. Several branches were always visi- 

 ble at the origin of the vessels from the carotid but the fibers 

 were lost in the dura before the posterior lobe was reached. 



However, it was finally possible to demonstrate nerve fibers 

 actually entering the posterior lobe along the artery. Certainly 

 the disparity between the nerve supply to the posterior and 

 anterior lobes is most striking — -in the anterior lobe almost super- 

 abundant, in the posterior lobe very few. This contrast may 

 in some measure be due to the difficulties mentioned above; we 

 are however disinclined to lay much emphasis on them. 



A most striking color contrast is demonstrated upon removing 

 the hypophysis after vital staining. The anterior lobe is a yel- 

 lowish white, the posterior a deep indigo blue, possibly due to 

 the (autogenic?) nervous character of the posterior lobe. The 

 blue is of a homogeneous character, no nerve fibers being differ- 

 entiable under the higher magnifications of the binocular micro- 

 scope. The intensity of the blue is even much more marked 

 than that of the adjacent, deeply staining oculomotor nerve. 



