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Show 1890.] HELODERMA SUSPECTUM. 171 ulnar side. To speak more strictly, this superficial muscle of the forearm does not altogether run down its outer side, but rather crosses the limb somewhat obliquely, from the proximo-radial side to the ulno-distal aspect. 43. Flexor carpi radialis.-This rather slender muscle, though it develops a strong tendon both at its origin and insertion, arises from the internal humeral condyle, and, passing down superficially, on that side of the forearm, it becomes inserted into the os carpi radiale, and furthermore sends a tendinous slip to be inserted into the proximal extremity of the pollex metacarpal. 44. The Pronator radii teres is a conspicuous muscle of some considerable bulk, which arises from the internal condyle of the humerus, by means of a strong tendon, and is inserted into the anterior surface of the shaft of the radius for fully half its length. It is fleshy at its insertion, and intimately related to the flexor carpi radialis for its entire length. 45. Pronator accessorius.-Mivart found this interesting muscle present both in the Iguana and in Parson's Chamseleon, but according to Sanders it is absent both in Liolepis and Platydactylus, and present in Phrynosoma. Hoffmann states that it is absent in Gonio-cephalus, and he terms the muscle the M. ulno-carpalis. Riidinger termed it the Pronator quadratusproprius ; Mivart gave it the name here adopted ; it is the Pronator radii brevis of Sanders, and the Ulno-navicularis of Fiirbringer. Heloderma suspectum has it arising from the anterior aspect of the internal condyle of the humerus by rather a slender tendon, whence it passes directly across to the radius to make a carneous insertion upon rather more than the middle third of the shaft of that bone, along a line upon its inferior aspect. The tendons of the biceps and the brachialis anticus pass between this muscle and the proximal third of the shaft of the radius, to their insertions. 46. Pronator quadratus.-Having removed the superficial layer of muscles from the anterior aspect of the forearm, we readily expose the present one. It is seen to be a fleshy plane of muscular fibres which obliquely span the inter-radio-ulnar space; arising from a line extending down the shaft of the ulna on its radial side, these fibres pass forwards to the radius and insert themselves on the entire length of its shaft, on the side opposite the ulna. Heloderma suspectum, then, possesses all three of these pronator muscles in its forearm, but we see from what has gone before that some lizards may have but one of them, others only two, and still others all three: so, then, we may judge that when the morphology of these Vertebrates is better known, these differences may come into play, as one good set of characters, in their classification. At the postero-external aspect of the distal end of the ulna, at the back of the carpus, there is found in Heloderma a concavo-convex bonelet which I take to be the "pisiform." Attention is drawn to this ossicle here as we shall have to refer to it iu the description of our next muscle. 47. Flexor perforans digitorum.-Before rendering my account |
