60 ANATOMY IN A NUTSHELL. 



LESSON XIII. 



Humerus.- (Plates XXII-XXIII.) — The humerus is the longest bone in 

 the upper extremity, and is the only one in the arm. hs upper extremity con- 

 i n head, neck ami two tuberosities, a greater ami lesser. The head is 

 directed inward, upward and backward: on this account one can lift his arm 

 higher when broughl a little forward than when at right angles to the body; the 

 head i- about a hemisphere. The contracted pari below the head is called the 

 anatomical neck; it is rarely broken, while the part below the tuberosity is 

 called the surgical neck on accounl of it being the seat of fracture. Between 

 the two neck- are the tuberosities, the greater on the outer aspect of the bone, 

 separated from the lesser by the bicipital groove which is for the long head of 

 the Biceps. 



The greater tuberosity has three facets, the upper one for the Supraspin- 

 atus muscle, the middle one tor the Infraspinatus muscle, and the lowerone for 

 the Teres minor. The lesser tuberosity is in the form of a cone and has at- 

 tached to it the Subscapulars. The bicipital groove extends about one-fourth 

 the way down the bone; its outer ridge is also anterior and is for the attach- 

 menl of the Pectoralis major: the inner ridge is posterior and is for the attach- 

 ment of tin' Too- major; the groove has the Latissimus dorsi attached. The 

 diaphysis is somewhat triangular on cross section and has three surfaces and 

 three borders. 



The anterior border extends from the front of the great tuberosity to the 

 coronoid depression below, separating the external from the internal surface.-; 

 it- upper part is the external bicipital ridge for the insertion of the Pectoralis 

 major muscle; the lower part is covered by the Brachialis anticus. The ex- 

 ternal border extends from the posterior part of the great tuberosity to the ex- 

 l condyle, and separate- the external and posterior surfaces; its lower part 

 i- the supracondylar ridge. From above downward it has attached the lower 

 pari of the Teres minor on the posterior aspect, the middle or long humeral 

 head of the Tricep.- separated from the short head of the same by the musculo- 

 spiral groove which transmits the musculo-spiral nerve and the superior pro- 

 funda artery. The external supracondylar ridge has attached the external 

 intermuscular septum which gives attachment to five muscles, viz., Deltoid, 

 Brachialis anticus, Triceps, Supinator longus, and Extensor carpi radialis 

 longior. The internal border extends from the inner part of the lesser tuber- 

 osity to the internal condyle, separating the internal and posterior surfaces. 

 From above downward it has the Teres major, and Coraco-brachialis. 



|{el<>\\ the Insertion of the Coraco-brachialis is the canal for the nutrient 

 artery, which run- toward- the distal extremity of the bone (Page 19, Lesson 

 3econd canal i- often presenl on the posterior surface; its artery comes 

 from the superior profunda. The internal intermuscular septum is attached to 

 the internal supracondylar ridge and has attached to it three muscles, viz., 

 Tricep-. Brachialis anticus, Coraco-brachialis, and occasionally a fourth mus- 

 cle. Pronator radii teres. The external surface gives attachment to the Del- 

 toid about two-fifth- or one-half the way down the hone, andbelow this to the 



