II. External Appearances of the Band.
When the bodies were suspended and placed face to face, it was evident that the congenital position had been secured. All observations were made, as far as was possible, with the bodies in this position. With it the details of structure, it was thought, could be easily understood; without it the subject would be difficult and confused.
The “band” was a massive commissure placed between the bodies at the junction of the abdominal and thoracic regions of each. It was broader above than below, and had a circumference of nine inches. It presented four surfaces for examination, an upper, lower, and two lateral surfaces.
The upper surface was somewhat flattened in both Chang and Eng. The ensiform cartilage of each body could be felt deflected from the sternum and prolonged into the band. The base of the cartilage in Eng presented a rounded circular eminence, measuring one inch in diameter. There was no corresponding eminence in Chang. The upper aspect of each process could be well defined beneath the skin, the subcutaneous connective tissue being more abundant in Chang than in Eng. The upper surface measured 2-1/2 in. in width at its base towards Eng, and 2-1/3 in. at its base towards Chang. It was 2 in. wide at its middle.
Fig. 2. The twins in the acquired position (E. R., C. L.), showing band and the primary incisions, a-b, c-d. From a photograph taken after death at Philadelphia.
The lower surface was much narrower than the upper. It was marked in the centre, but nearer the anterior than the posterior border, by a linear scar one inch in length, which it was thought answered to the position of the single umbilicus. The skin was adherent at this point, but elsewhere was easily raised in folds. Behind the scar, i. e., toward the posterior part of the band, the skin was somewhat corrugated. This portion answered, in position, to Chang’s umbilical pouch.
The lateral surfaces. The terms upper surface and lower surface have fixed values, no matter how they may be approached by the observer. This is not the case, however, with the lateral surfaces, as will appear from the following considerations. Viewing the band as a separate form—as it was spoken of during the life of the twins—we will see that the terms front (“anterior”) and back (“posterior”), as given to the lateral surfaces, were derived from studying the acquired position. Thus we were bound not to cut the “front” of the band, but allowed to make an incision on the “back.” Now this position of selection was destroyed, and its terms deprived of what meaning they may have had, by the reproduction of the congenital relations of the bodies.
There is no doubt that in infancy and early childhood there was no acquired position, and, therefore, neither “front” nor “back” to the band. And later, when, as we have reason to believe, the position of selection was gradually adopted, the terms “front” and “back” were reversible—the “front” meaning that which corresponded to the surface of least thoracic approximation. Thus when the adult condition was fixed, and the “front” answered to the widely separated right side of Eng’s chest and left side of Chang’s chest, the “back” was in relation with the closely approximated left side of Eng’s chest and right side of Chang’s.
To avoid awkward repetition of phrases expressing the facts of the last sentence, the following characters will be employed in describing the “lateral” surfaces of the band.
E. R., C. L. (Eng’s right, Chang’s left) will designate the “anterior” surface of the acquired position. C. R., E. L. (Chang’s right, Eng’s left) will designate the “posterior” surface. Since the right side of Chang’s half of the band merged into the left on Eng’s half, while the right side of Eng’s half, after it passed the middle line, became the left half of Chang’s, we propose using the characters E. L., E. R., and C. R., C. L., which will be understood as signifying left side Eng, right side Eng, etc.
Using the above signs we found that the surface E. R., C. L. was inclined decidedly downward and backward when seen in the congenital position, and was 3 in. high and 2-1/2 in. wide. At E. R., the border answering to the ensiform cartilage was marked by a large rounded tubercle; it was much more pronounced than on the corresponding border of C. L. When seen in the acquired position, E. R., C. L. became “anterior,” when, at its upper margin, C. L. was longer than E. R. by one-half inch. The tubercle on E. R., already noticed, was much more prominent than C. L. The contour of the inferior margin was also different, being more uneven. C. L. was not only longer, but was more obliquely placed downward and outward to the centre of the band than E. R. (See cast in the Mütter Museum.)