The anatomy of the human skeleton / by J. Ernest Frazer.

  • Frazer, John Ernest Sullivan, 1870-1946.
Date:
1920
Catalogue details

Licence: In copyright

Credit: The anatomy of the human skeleton / by J. Ernest Frazer. Source: Wellcome Collection.

    138/396 (page 88)
    The concavity on the back of the condyle contains the ulnar nerve and inferior profunda artery. Observe that, owing to the disposition of the front fibres along the lower border of the condyle, the internal lateral ligament has a sort of concavity or groove on its superficial posterior aspect, opening out to the forearm, and the groove on the back of the condyle leads the nerve into this, so that it enters the forearm on the internal ligament, behind the anterior fibres. This portion of the bone on which the nerve lies is formed by an extension of ossification from the shaft, so cutting off the epiphysis of the epicondyle from the three centres that form the “ epiphysis of the lower end ” (Fig. 64). The external condyle (Fig. 68) has a rough surface looking outwards for the external lateral ligament of the elbow : the superficial extensors of the forearm are fused with the upper part of this, and so take origin here from the upper portion of the rough surface and from the point of bone above. The surface traced back becomes rapidly but irregularly smaller in area, being only linear along the margin of the capitulum where the fibres are those of the posterior capsule : from this the line of capsular attachment turns up sharply at a right angle along the margin of the trochlea. Included in the angle is the origin of Anconeus, while the point of the angle projects slightly (Fig. 68) between capitulum and trochlea, marking the attachment of the cruciate ligament, a band running in the capsule to the back margin of the lesser sigmoid cavity of the ulna and marking the remnant of the original division between the radial and humero-ulnar joints. • The trochlea and capitulum are placed in a plane somewhat in front of that of the shaft : the outer supracondylar ridge is turned forward with the condylar mass to correspond with this disposition, but the inner ridge, though it shows a slight forward tendency in its upper part, is turned rather backwards below in conformity with the slight backward direction of the condyle on to which it is continued. The trochlea is only covered with articular cartilage over part of its extent, as is easily seen on the bone (Fig. 63) : its cartilage-covered surface is broadest behind, in accordance with the comparative breadth of the olecranon that articulates with it here. When, therefore, the forearm is flexed, the broad olecranon overlaps by its outer border the inner part of the capitulum, and the ulna tends to move radialwards, moreover, as a result of the disposition of the surface of the trochlea. The inner part of the trochlea is deeper than the outer, so that the axis of the whole surface made up of these two parts is set obliquely across the vertical axis of the shaft. The result of this is seen when the forearm is extended to the full and it is apparent that the line of the forearm does not coincide with that of the arm : the angle is modified by various factors in the forearm, but that made between the axes of trochlea and humerus is about 105 degrees in male and 108 degrees in female bones. The inner vertical surface of the trochlea is covered by synovial membrane and has no ligamentous fibres attached to it , in fact the whole structure might be described as intra-articular in position. The capitulum is altogether covered by hyaline cartilage, and is spheroidal to permit of a gliding movement of the head of the radius during flexion and extension, and a rotating movement of the head on it during pronation and supination. Its centre is the first to appear at the lower end of the bone. The upper end of the bone lies below and, for its greater part, external to and in front of the end of the acromion, and can be appreciated by the fingers through the Deltoid. In a thin arm it is possible to feel the small tuberosity through the anterior fibres of this muscle : when the arm is hanging by the side, the bicipital groove lies vertically below the tip of the acromion, but, by eversion of the arm, this groove and