THOKACIC LIMBS 



563 



FIG. 436. 



The bicipital groove is narrow, and its lips, or bicipital ridges, are 

 prominent ; to the outer lip is attached the pectoralis major muscle ; to 

 the inner lip the latissimus dorsi and teres major 

 muscles. In a fossa at the upper end of the 

 groove, the fovea capitis, is inserted the gleno- 

 humeral ligament. The lesser tuberosity is 

 more prominent than in the cat. On a smooth 

 space on its upper surface is inserted the sub- 

 scapularis muscle. 



The shaft is cylindrical above, but flattened 

 from before backward below. The inner aspect 

 is crossed from behind downward and forward by 

 a wide musculo-spiral groove for the musculo- 

 spiral nerve and the deep brachial vessels. The 

 oblique disposition of these structures and the 

 different planes of the articular extremities are 

 the results of a torsion of thirty degrees which 

 has taken place in the humerus round its long 

 axis during development. The shaft presents 

 three borders, anterior, external, and internal, 

 and three surfaces, external, internal, and pos- 

 terior. The anterior border runs downward 

 from the outer lip of the bicipital groove and 

 ends between the capitellum and the trochlea, 

 The external border extends from the posterior 

 border of the greater tuberosity to the outer 

 condyle. It is crossed by the musculo-spiral 



groove ; its lower end is termed the external supracondyloid ridge. 

 The internal border begins above as the inner lip of the bicipital 

 groove and ends as the internal supracondyloid ridge. At its middle 

 it is roughened for the insertion of the coraco-brachialis muscle. 

 Below this area is the nutrient foramen. The external surface lies 

 between the anterior and external borders. Above the middle is the 

 rough deltoid ridge, and below it the musculo-spiral groove. The 

 internal surface (sometimes called the anterior surface) is between the 

 anterior and internal borders. Its upper part is the bicipital groove ; 

 from its lower part arises the brachialis anticus muscle. The posterior 

 surface is between the internal and external borders. It is smooth ; 



na 



LEFT HUMERUS. VIEWED IN 

 FRONT. 



1, shaft; 2, head; 3, neck; 4, 

 greater tuberosity; 5, lesser tu- 

 berosity; 6, bicipital groove; 7, 



8, ridges bounding the latter and 

 giving attachment to muscles ; 



9, position of insertion of the 

 deltoid muscle ; 10, principal nu- 

 trient foramen; 11, capitellum 

 for the radius; 12, trochlea for 

 the ulna; 13, 14, external and in- 

 ternal epicondyles ; lf>, 10, supra- 

 condyloid ridges; 17, fossa for 

 the coronoid process of the ulna. 



