THE SCAPHOID. 425 



constricted portion, much broader transversely than vertically, connecting the head 

 with the body. It often presents a groove along the upper and inner aspect near 

 the articular surface of the head for the insertion of the ligament passing to the 

 scaphoid. The head, which points forward and inward, is articular in front and 

 below. The anterior surface, which fits into the hollow on the back of the scaph- 

 oid, is vaguely oval, with its long axis running downward and inward. The upper 

 edge, parallel with this, is nearly straight. The articular surface of the head ex- 

 tends onto the under side, reaching to the deep groove separating the neck from 

 the posterior facet for the calcaneum. On a fresh bone the cartilage shows the 

 following facets, which are less well marked on a macerated one : a facet on the 

 front of the head to fit into the scaphoid ; one on the lower and inner side to 

 rest on the anterior articular facet of the top of the calcaneum ; one partly between 

 these, which in the dried bones would be free, appearing between the sustentaculum 

 and the scaphoid, but in life resting on the inferior calcaneo-scaphoid ligament, 

 which is partly covered with cartilage and elsewhere with synovial membrane, 

 forming a part of the socket. The cartilage on this surface is distinguished by its 

 thinness. These facets are modified according to the arrangement of those on the 

 calcaneum. If there be but one long anterior facet on both sustentaculum and on 

 the end of the body of the calcaneum, the facet on the head for the anterior facet 

 of the calcaneum reaches that for the concavity of the scaphoid in front, leaving 

 internally a triangular interval between the two, occupied by the facet for the liga- 

 ment (Fig. 437)- In the other extreme (Fig. 438), where the anterior facet on 

 the calcaneum does not reach beyond the sustentaculum, the area of the head rest- 

 ing against the ligament completely separates the two others and plays on that part 

 of the calcaneum where the anterior articular cartilage should be. Finally, when 

 the anterior facet on the calcaneum is divided into two, the corresponding facet may 

 be completely subdivided by an interruption of the cartilage, or in less marked 

 forms there may be merely a ridge breaking the surface into two, but without sepa- 

 ration ; such a ridge is often found even when the opposed articular surface is not 

 divided. The lines, however, on the head of the astragalus do not strictly correspond 

 to the boundaries of these surfaces. The astragalus articulates with four bones, — the 

 tibia, fibula, calcaneum, and scaphoid. 



Development. — The nucleus probably appears at about the seventh month of 

 foetal life. When the os trigonum occurs, that implies another centre for the ex- 

 ternal tubercle and the part of the articular surface under it. 



The deviation of the axis of the neck from that of the long axis of the bone 

 varies considerably among individuals, but, nevertheless, changes during develop- 

 ment. In the adult the angle varies from o to 24°, the mean of forty-three bones 

 being 12.32°. In the foetus (presumably at term) the angle ranges from 17.5° to 

 45.5°, the mean of twenty-two bones being 35.76*^ 



•o 1 



THE SCAPHOID. 



The scaphoid,'' or navicular, may be compared to a disk, concave behind where 

 it fits onto the head of the astragalus, convex in front where it rests on the three 

 cuneiform bones. It is thinner at the outer end, where it touches the cuboid, than 

 at the inner, where it presents the tuberosity. The superior, or dorsal, surface 

 is long transversely. Its posterior border is regularly concave, the anterior slightly 

 scalloped, presenting two small points projecting forward on either side of the mid- 

 dle cuneiform. When in position the highest point on the scaphoid is behind that 

 bone. The greater part of the dorsal surface slants downward on the inner side of 

 the foot. The inferior, or plantar, surface is rough, and in the main transversely 

 concave. The tuberosity at the inner border for the attachment of a part of the tibi- 

 alis posticus muscle is a knob formed by the junction of the dorsal and plantar sur- 

 faces, and projecting downward chiefly into the sole of the foot. The end of the 

 knob is sometimes distinct from the scaphoid, and is known as the tibiale externum. 



^ C. L. Scudder : Congenital Talipes Equino-Varus, Boston Med. and Surg. Journ., vol. 

 ii., 1887. Parker and Shattock : The Pathology and Etiology of Congenital Club-Foot, London, 

 1884. 



- Os naviculare pedis. 



