On parts of the skeleton of a mammal from Triassic rocks of Klipfontein, Fraserberg, South Africa (Theriodesmus phylarchus, Seeley), illustrating the reptilian inheritance in the mammalian hand / by H.G. Seeley.

  • Seeley, H. G. (Harry Govier), 1839-1909.
Date:
1888
Catalogue details

Licence: Public Domain Mark

Credit: On parts of the skeleton of a mammal from Triassic rocks of Klipfontein, Fraserberg, South Africa (Theriodesmus phylarchus, Seeley), illustrating the reptilian inheritance in the mammalian hand / by H.G. Seeley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    The fourth metacarpal is 5 millims. wide proximally, contracts to 4 millims., and expands distally to 9 millims.; but, though these transverse measurements are the same as in the third, the configuration of the bone is different, because the distal widening is here gradual from the proximal third of the bone, while the third meta- carpal widens rapidly near the distal end. A short ridge descends obliquely from the inner angle of the proximal articulation. The fifth metacarpal bone has its proximal articular end directed inward. It is 6 millims. wide, the distal end is about equally wide, and in the middle the shaft contracts to between 3 and 4 millims. The inner lateral border is nearly straight, except that there is a marked concavity below the articulation, which may result from the inflexion of the inner proximal angle, such as is seen in the fourth meta- carpal. Distally there is some appearance of a ridge on the superior inner border of the bone. The Digits. The digits are imperfectly preserved. In each the first phalange is large and strong, but the other phalangeal bones are short. In the fifth digit there are three phalanges, and the fourth has the same number, but the third appears to have had four phalanges. In the second digit only two phalanges are preserved, and the first has but one preserved and a second indicated. In the first digit the first phalange is 8 millims. long. It is wide at the proximal end, where the articulation is concave from side to side. It appears to have a well- developed anterior end, with a rounded articulation, margined superiorly by a slight groove. In close contact with this surface is a small hemispherical ossification which appears to represent a second phalange. In the second digit the stout first phalange is 12 millims. long. It is 7 millims. wide proximally and 5 millims. distally, but contracts rapidly below the proximal articulation. The second phalange is similar in form, but smaller, being 7 millims. long. Its distal extremity appears to have been articular, but there is no trace of a third phalange, which may have been preserved in the counterpart slab. In the third digit the first phalange is relatively long and slender. It measures 13 millims. in length, is 8 millims. wide proximally, and about half as wide distally. The second phalange is hardly more than 3 millims. long; and the third is nearly 7 millims. long. It has a good trochlear distal end, and beyond it is an indication of a fourth bone, but there is no evidence to show whether it was a complete phalange. In the fourth digit the first phalange is 15 millims. long, so that the first phalangeal bones follow the same law of progressive elongation as the metacarpals. The bone is rather stouter than the others, being less contracted distally. The second phalange is about 3 millims. long, but more than 5 millims. wide. Anterior to this is a curved mass of most irregular form, with a striated surface, which I regard as being the extremity of the digit, but the absence of definition of the joints leads me to believe