SHOULDER, ARM, FOREARM, AND HAND. 169 



The neck of the radius located above the bicipital tuberosity. 



The oblique line of the radius a very important structure. 



The styloid process, with base and apex for ligament and muscle. 



The sigmoid cavity, for articulation with the head of the ulna. 



The semilunar and scaphoid articular surfaces. 



The nutrient foramen, directed upward according to rule. 



The interosseous border, for the interosseous membrane. 



The anterior surface, occupied by deep flexor muscles. 



The posterior surface, occupied by deep extensor muscles. 



The outer surface, occupied by muscles. 



Describe tlie anterior surface of the radius. 



The oblique line of the radius extends from the bicipital tuberosity to the 

 insertion of the pronator radii teres on the outer border of the bone. (Fig. 124.) 

 This line may be viewed as consisting of three lips : (i) An upper one, into which 

 the supinator brevis is inserted ; (2) a middle one, from which the radial head 

 of the flexor sublimis digitorum muscle takes its origin ; (3) an inferior one, from 

 which the flexor longus pollicis takes its origin. This surface gives origin 

 below the oblique line to the flexor longus pollicis and insertion to the pronator 

 quadratus. 



Wliat can you say of the external surface of tJie radius ? 



Its upper one-half is occupied by the supinator brevis and pronator radii teres ; 

 its lower one-half is overlapped by the radial extensors of the carpus, and crossed 

 by the extensor ossis metacarpi pollicis and extensor brevis pollicis ; this latter 

 muscle is also called extensor primi internodii pollicis. 



What can you say of the posterior surface of the radius f 



Its upper one-third gives origin to the radial part of the extensor ossis meta- 

 carpi pollicis and the extensor primi internodii pollicis ; the part of the bone 

 below this is covered by the tendons of the two preceding muscles. 



The Ulna. (Fig. 124.) 



Name the important bony parts of the ulna and give their importance in prac- 

 tical anatomy. 



The olecranon process, for the insertion of the triceps muscle. 



The coronoid process, for the insertion of brachialis anticus muscle. 



The greater sigmoid fossa, for articulation with the humerus. 



The lesser sigmoid fossa, for articulation with the radius. 



The oblique line, for attachment of the supinator brevis muscle. 



The interosseous ridge, for attachment of the interosseous membrane. 



The styloid process (apex), for internal lateral ligament of wrist. 



The head articulates with the ulnar sigmoid cavity of the radius. 



The base of the styloid process, for the insertion of the supinator longus. 



The anterior surface of the ulna is for muscular origin. 



The inner surface of the ulna is for muscular origin. 



The posterior surface of the ulna is for muscular origin. 



Explain the anterior surface of the ulna. 



It has the nutrient foramen, which, according to the rule, is directed toward 

 the elbow. It gives origin to the flexor profundus digitorum and pronator 

 quadratus muscles. This surface is limited by the anterior border, the interos- 

 seous border, and an oblique line. 



What can you say of the internal surface of the ulna ? 



It is occupied by the flexor profundus digitorum in its upper three-fourths ; 

 the remainder of this surface of the ulna is subcutaneous. 



What can be said of the posterior surface of the ulna ? 



This is the most difficult part of the bone, but must be mastered before you 

 can appreciate the attachment of certain muscles. This surface is subdivided by 



