THE ULNA. 187 



that, we observe a smooth concavity, where the beginning of 

 the flexor digitorum profundus sprouts out. 



The external angle of the triangular part of the ulnajs very- 

 sharp, where the ligament that connects the two bones is fixed ; 

 the sides which make this angle are flat and rough, by the ac- 

 tion and adhesion of the many muscles which are situated 

 here. At the distance of one-third of the length of the ulna 

 from the top, in its forepart, the passage of the medullary ves- 

 sels may be seen slanting upwards. The internal side of the 

 bone is smooth, somewhat convex, and the angles at each edge 

 of it are blunted by the pressure of the muscles equally disposed 

 about them. ' 



As this bone descends, it becomes gradually smaller ; so that 

 its lower end terminates in a little head, standing on a small 

 neck : towards the inner and back part of which last, an oblique 

 ridge runs, that gives rise to the pronator radii quadratus. The 

 head is sometimes cylindrical, smooth, and covered with a car- 

 tilage on its external side, to be received into the semilunar 

 cavity of the radius ; which a styloid process rises from its in- 

 side, to which is fixed a strong ligament that is extended to the 

 os cuneiforme and pisiforme of the wrist. At the root of the 

 process, the end of the bone is smooth, and covered with a car- 

 tilage. Between it and the bones of the wrist, a doubly con- 

 cave movable cartilage is interposed ; which is a continuation 

 of the cartilage that covers the lower end of the radius, and is 

 connected loosely to the root of the styloid process, and to the 

 rough cavity there ; in which mucilaginous glands* are 

 lodged. 



The ulna is principally concerned in the articulation with the 

 os humeri, and forms a hinge-like joint, which allows extension 

 nearly to a straight line, and flexion to an acute angle. By the 

 sloping of the pulley-like surface, the lower part of the arm is 

 turned outwards in the extension, and inwards in the flexion ; 

 which greatly facilitates the motion of the hand towards the 

 head. 



* All these so called glands are m.ere masses of adipose matter, supposed, 

 though wrongly by Havers to be the glands which secrete the synovia. P. 



