NERVUS TERMINALIS : MAMMALS 51 



These fibers are unmyelinated, and correspond in appearance 

 with those previously described in the cerebral vessels of the 

 cat. They are present at various levels of the muscular coat 

 of the arterial wall, as shown in cross-sections. They send their 

 twigs between the smooth muscle cells in the typical manner of 

 motor tenninations in this type of muscle. As previously stated, 

 it seems probable that they should be regarded as motor endings. 



The terminations which have been designated as Type II are, 

 as in the cat, strikingly different in appearance (fig. 39, A and B) 

 from those of Type I. The nerve fiber leading to these is mye- 

 linated, as indicated by a reddish cylinder surrounding the pur- 

 phsh-black of the central axis. The myelin sheath in most 

 cases continues almost to the spindle-shaped termination. The 

 axis, after emerging from the sheath, divides into two or three 

 main rami which give ofT a varying number of short processes. 

 These processes terminate invariably in rounded knobs. The 

 portion of the spindle-shaped organ which was not occupied by 

 these processes appeared nearly clear or had a slight bluish tint 

 and was slightly granular. It stood out in strong contrast to 

 the purplish red of the surrounding muscle cells. 



The spindles in the beef showed considerable variation in size. 

 Of those measured, the smallest were 4 m in diameter and 12 m 

 in length. The largest were 6 m to 7 m in diameter and 35 /x in 

 length. The majority appeared to be about 5 m by 25 m to 30 

 /x. Figure 39 illustrates one of the largest observed (A) and also' 

 an example of the smallest size (B) drawn to the same scale. It 

 will be noted that the two end-organs represented in figure 39 B 

 are the terminations of what appeared to be a branch of the 

 larger fiber shown in the figure. A node is seen in the myehn 

 sheath, through which the branch to these terminal organs passes. 

 In a few instances it was possible to follow the myelinated fiber 

 to the external surface of the artery and for a little way beyond. 



3. The nervus terminalis of the mule and the horse 



The mule. As represented in figure 40, the nervus terminalis 

 of the niule runs parallel to the olfactory tracts, between them 

 and the sagittal fissure of the brain. The nerve in both the mule 



