Humphrey, Brain of the Snapping Tiutle. 95 



drawn with the camera lucida. These two cells were chosen as 

 typical of this group in the turtle. As shown in the figure they 

 are not in this form unipolar but bipolar and in some case I 

 think even tripolar. The protoplasmic (?) process branches a 

 short distance from the cell. This process is directed toward 

 the periphery. The small process from the base is supposed to 

 be the axis cylinder. The direction of the axis cylinder pro- 

 cesses I was not able to ascertain. These cells are similar to 

 those found in the brains of other turtles that I have examined. 



Commissures of the Mesencephal. The post commissure 

 forming the cephalic limit of the mesencephal is broad and 

 strong, formed of fibers that pass laterad and slightly caudad 

 into the ventral portion of the mesencephal. In the roof of the 

 mesocele is a narrow commissure extending from near the post 

 commissure caudad for about two thirds of the length of the 

 tectum (Fig. 6). This commissure is often called the commis- 

 sure of the tectum, but Stieda first gave it the name of Sylvian 

 commissure and this has been adopted in this paper. Near the 

 cephalic limit of the mesencephal in its ventral floor is found 

 another commissure. The fibers of this commissure penetrate 

 between the roots of the oculo-motor nerve and through the 

 bundle of the posterior longitudinal fasciculus. (Fig. 21). This 

 commissure is of two parts, the more ventral part is the broadest 

 and extends laterad and disappears, spreading diffusely in the 

 peduncular region. To this commissure Stieda applies the 

 name inferior commissure, but this name is open to the objection 

 that it is more usually applied to the commissure of the infun- 

 dibulum. Osborn calls it the superior infundibular commissure, 

 but in the turtle it is not connected with any part of the infun- 

 bular wall. In this paper it is not named but is shown at x in 

 figures 6, 7. In the vicinity of this commissure the posterior 

 longitudinal fasciculi from a prominent decussation. 



Diencephal. 



The Roof of the Diencephal} — In 1882 Rabl-Riickhard and 



! Since this was written Sorensen's admirable resume of the literature of the 

 subject was received. 



