waite: plexi of nectueus. 73 



Nerve i (Fig. 1) is sleuder, and does not contribute to the innerva- 

 tion of the appendage, but is distributed to the inner wall of the girdle. 

 It often lies close to nerve ii, and may (six cases in thirty) anastomose 

 with it. 



Nerve ii is also slender, and is distributed to the same region as is i. 

 It seems questionable if i and ii can be properly considered parts of the 

 plexus. In strength they approximate the ordinary post-brachial spinal 

 nerves (vi to xv). In some cases branches of ii run in close relation to 

 the supracoragoid (su'crac.) branch of iii, and may (four cases in thirty) 

 pass out through the coracoid foramen with the supracoracoid. In no 

 case have I found any anastomosis between branches of ii and iii, as im- 

 plied by Hoffman ('74, p. 229) in his account of Necturus (Menobranchus); 

 and from my specimens of Xecturus I can assert that this is certainly 

 not a constant relation, if indeed it occur at all. 



Nerve iii usually divides into three branches, of which the small 

 anterior one is distributed to the thoracic wall, the middle one forms the 

 supracoracoid nerve (su'crac), while the larger posterior branch enters 

 the main trunk of the plexus. 



Nerve iv is usually the strongest trunk of the plexus. It passes 

 directly to its exit posterior to the scapula, close to the margin of the 

 glenoid cavity, giving off in its course a single small branch, which is 

 distributed anteriorly on the thoracic wall. Before reaching the border 

 of the scapula this nerve usually divides into two main branches, which 

 pass side by side to the musculature of the anterior appendage. 



Nerve v is the most posterior nerve to enter the plexus, its anterior 

 branch joining nerve iv just before this reaches the scapula, while the 

 small median and the posterior branches are distributed to the body wall, 

 posterior to the girdle. 



There were no variations of note in the topograph?/ of the plexi in the 

 thirty animals examined, except in one case of slight want of symmetry in 

 the point of junction of v with iv, but this occurred in a specimen which 

 was normal in its sacral structures. Some variation occurs in the rela- 

 tive strengths of the nerves ; for while iv is usually the strongest, it may 

 be equalled by iii, as was seen in six cases, of which four were with the 

 ■sacrum in a normal position (19th vertebra), one with the sacrum on 

 the 20th vertebra, and one with an unsymmetrical sacrum (Plate 2, 

 Fig. 5). Again, nerves in and v are usually of about equal strength, 

 but III may be much (six to eight times) stronger than v, or more 

 rarely may be weaker. 



These conditions show a tendency toward variation in the location of 



