1890.] HELODERMA SUSPECTUM. 213 



wards the trunk of the seventh spinal nerve, we observe that the 

 first branch that it gives off is a short thick one, which it sends to 

 join the main stem of the sixth, and this branch crosses the branch 

 sent to the nerve now under consideration by the sixth, which is the 

 branch described in the last paragraph. In other words, the sixth 

 and seventh trnnks are mutually joined to each other, near their 

 middles, by rather short thick branches which cross each other. 

 Below this point, and still following the trunk of the seventh spinal 

 nerve, we note that it soon thereafter joins with and merges into the 

 trunk of the eighth spinal nerve, and gives off no branches before so 

 doing. No branches are given off from the trunk of the eighth spinal 

 nerve before its mergence with the trunk of the seventh, and the two 

 below that point constitute a still larger trunk, which upon arriving 

 at the axilla passes on down the arm, breaking up as it does so into the 

 more usual branches that go to supply the muscles of the brachium, 

 antebrachium, and the hand. 



It is hardly necessary to add that the vessels, the subclavian vein, 

 and the brachial artery are situated ventrad to this nervous plexus 

 of the brachium. 



Upon comparing this arrangement of the nerves in the brachial 

 plexus of Heloderma with the descriptions and figures as given us 

 by Hoffmann (45) of such species as Platydactylus (Bgyptiacus, 

 JJromastix spinipes, Pseudopus pallasii, Chamceleon vulgaris, or even 

 Crocodilus acutus, I fail to find scarcely any agreement whatever, 

 and it is only in such a form as Uromastix that we note any 

 approach to what we find in Heloderma. This agreement refers to 

 the number of nerves and their connections that go to form the plexus ; 

 but even in these particulars the two species are at variance, though 

 in both four spinal nerves constitute the plexus, they being vi-ix in 

 Uromastix and v-viii in Heloderma. 



Next we come to consider the lumbosacral plexus, and there is no 

 doubt but that quite as much inconstancy of arrangement exists here 

 as we noted above with reference to the brachial interlacement. 

 Indeed, Mivart included the sacral plexus in his remarks as we 

 quoted him above, and my own observations go to sustain the opinion 

 he has expressed in the premises. 



Using the same specim.eu oi Heloderma as we did in our examina- 

 tions of the brachial plexus, and still confining ourselves to the right 

 side of the animal, the following arrangement of the nerves is to be 

 made out. There are two vertebrae in the sacrum of this lizard, and 

 there are three nerve-trunks that enter into the formation of the 

 lumbo-sacral plexus. The spinal nerve that emerges from the inter- 

 vertebral foramen between the last two lumbar vertebrae is a small 

 one, and it immediately divides into two delicate branches. Of these 

 the anterior one goes to supply the muscles in the vicinity, while 

 the posterior branch trending backwards joins, at about its middle, a 

 much larger spinal nerve that comes out from the spinal cord between 

 the last lumbar and first sacral vertebrae. This latter, beyond this 

 point, in turn merges with that spinal nerve that emerges from be- 

 tween the two sacral vertebrae ; and the common trunk thus formed 



