OCR Text |
Show 1890.] HELODERMA SUSPECTUM. 227 millimetres long. At the middle of this, upon its dorsal aspect, is found a small pit that has the appearance of an incompleted foramen. This character is constant. Both the radius and ulna long retain, at their distal and proximal extremities, the evidences of the epiphysial sutural traces. Sub-cylindrical in form, the shaft of the radius is but very slightly bent, and its enlarged distal end is moulded to articulate with the radial ossicle of the carpus. Its proximal extremity is also enlarged, cup-shaped at its summit, and flattened at the ulnar aspect of its head so as to be brought close against the corresponding extremity of that bone when the skeleton of the arm is properly articulated. The ulna, nearly as large as the radius in point of size, has a compressed shaft, with a very conspicuous, semiglobular, articular condyle at its distal extremity. At the other end of the bone the olecranon is well-developed, and a " greater sigmoid cavity " handsomely excavated. What is interesting here is the fact that no "lesser sigmoid cavity " is formed to admit in articulation the head of the radius, which latter is placed at the expense of a flattening in order to articulate with an apposed flat surface on the ulna, which occurs at the site of the " lesser sigmoid cavity " as it is presented to us in anthropotomy. Thus it will be seen that a sliding movement is admitted of here, but not a rotary motion on the part of the head of the radius, as is the case in many of the higher Vertebrata. Five carpalia represent the distal row of ossicles in the wrist of Heloderma, while proximally we find the ulnare, the radiate, and a centrale. Careful search, aided by a good lens, failed to discover any evidences whatever of the presence of an intermedium, much less the vestiges of any rudimentary digit. In a previous section, the large sesamoid that occurs in the great flexor tendon as it passes over the carpus has already been described ; and ligamentously attached to tbe outer side of the ulna is a large pisiform. As to articulations, two of the carpalia extensively articulate with the ulnare and with each other, while the inner one of the two is in contact extensively with the middle ossicle of this distal row. This last-named one in turn engages the entire inner surface of the ossicle of the carpalia upon its radial side, while its proximal apex comes slightly in contact with the centrale. Number four of the carpalia engages the entire distal surface of the centrale, but barely touches the last ossicle of the distal row upon the radial side. This one is devoted to the radiale and also articulates with the centrale. Proximally, the centrale articulates with the ulnare and radiale. Finally, it is hardly necessary to mention that the carpalia, as a rule, each engage a metacarpal distally, while radiale and ulnare articulate with the radius and ulna, respectively. The joints of the several digits of the manus remind us considerably of the corresponding parts as we find them in the toes of small ordinary existing birds, more especially the distal ones. Counting the claw in each case, w e note that the first finger upon the ulnar side possesses three joints ; the next one to it has five ; the middle one has four; the next one, radiad, has three ; while, finally the radial |