Anatomy of Hereditary Bovine Syndactylism. II. Muscles, Tendons, and Ligaments

Muscle, tendon, and ligament anomalies that distinguish externally 1) normal overlap sy/sy homozygotes from normal +/sy and +/+ animals; 2) normal +/sy animals from +/+ animals; and 3) syndactylous animals possessing the sy gene from other syndactylous animals were sought in the limbs from 35 syndactylons sy/sy, two normal overlap sy/sy, and six normal +/sy Holstein cattle.Tendons and ligaments were adapted to the single digit.Three digital extensor muscle tendons fused at the fetlock into a wide aponeurotic plate that received on each side a reinforcing branch from the deep suspensory ligament and inserted on the second and third phalanx.The tendons of the superficial and deep digital flexor muscles usually remained undivided and inserted normally on the single functional digit.A small branch often passed from the tendon of the superficial digital flexor muscle to the lateral dewclaw, the only anomaly of the front feet of normal overlap and of two of six +/sy animals.Other rarer muscle tendon branches to the dewclaw were found.The superficial part of the suspensory ligament, besides joining the tubular portion of the superficial digital flexor muscle tendon, attached by a wide band to the proximal sesamoid bones.Branches of the deep suspensory ligament were fewer than normal.As noted in the first paper in this series (1), control of the incompletely penetrant, recessive U.S. Holstein form of syndactylism may be facilitated by knowledge of anatomic differences that distinguish externally 1) normal overlap sy/sy homozygotes from normal +/sy and +/+ animals; 2) normal +/sy animals