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Show 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 trunks 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 cegyptiacus, Uromastix 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 tbe 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 specimen oi Heloderma as we did in our examinations 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 vertebras 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 intervertebral foramen between the last two lumbar vertebras 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 vertebras. This latter, beyond this point, in turn merges with that spinal nerve that emerges from be-ween the two sacral vertebrae ; and the common trunk thus formed |