72 ANATOMY IN" A NUTSHELL. 



cles attached to it and the ulna fourteen. Although there are twenty-three 

 muscles attached to these two bones, yet there are but twenty muscles in the 

 forearm, the Triceps, Biceps, and Brachialis anticus are in the arm (between 

 the shoulder and elbow.) The elbow-joint isdescribed in Lesson XIII. 



LESSON XVI. 



The Radius (Plates XX IV-XXV) is theshorterof thetwo bones of the fore- 

 arm. Its distal extremity is larger than that of the ulna, while its proximal extrem- 

 ity is smaller than that of the ulna. Thesetwo boneslie parallel. The proximal 

 extremity has a head, neck, and tuberosity; the circumference of the head is 

 concave, tts inner portion which articulates with the lesser sigmoid cavity of 

 the ulna is broader than the remaining portion which articulates in the orbicu- 

 lar Ligament. The upper surface of the head is also concave for the articula- 

 tion of the capatellum or radial head of the humerus; it is covered with cartil- 

 age in the recent state. The neck is the constricted part below the head; the 

 proximal part of the neck is surrounded by the distal part of the orbicular lig- 

 ament and distally it gives attachment to the Supinator brevis externally. The 

 bicipital tuberosity is distally from the neck at the antero-internal aspect of the 

 bone. It has a rough posterior portion for the insertion of the tendon of the 

 Biceps, and a smooth anterior portion for a bursa which is between the tendon 

 and the bone. The shaft is triangular on cross section and has three borders 

 and three surfaces. The anterior border extends from the bicipital tuberosity 

 distally to the outer aspect of the bone, then to the anterior border of the sty- 

 loid process. The proximal one-third of this border is the oblique line of the 

 radius; it separates the Supinator brevis from the Flexor longus pollicis, and 

 gives a1 tachmenl to the third head of the Flexor sublimis digitorum ; it separates 

 the anterior surface from theexternal surface. The inner or interosseous bor- 

 der, extends from the posterior pail of the bicipital tuberosity proximally to 

 the sigmoid cavity of the radius; its distal part divides into an anterior and 

 posterior portion and has the interosseous membrane attached to most of its 

 extent; it separates the anterior from the posterior surface. The posterior 

 border which is well marked in the middle one-third, extends from the back 

 pari of the neck of the radius to the middle tubercle on the posterior aspect of 

 the distal extremity; it separates the posterior from the external surface. The 

 anterior surface is concave at the proximal extremity and smooth at the distal 

 extremity. 



The proximal three-fourth gives attachment to the Flexor longus pollicis, 

 and the distal one-fourth to the Pronator quadratus. Where the proximal one- 

 third joins the middle one-third, is the nutrient foramen which is directed to- 

 wards the elbow. The nutrient artery is a branch of the anterior interosseous. 

 'I'h. posterior surface is convex from the proximal to the distal extremity; it 

 is covered by the Supinator brevis. Extensor ossis metacarpi pollicis, Extensor 

 brevis pollicis. and the distal one-third is covered by tendons. The oblique line 

 marks the proximal limit of the Extensor ossis metacarpi pollicis. The exter- 



