1 88 A MANUAL OF ANATOMY 



spiral groove, for the musculo-spiral nerve and superior profunda 

 vessels. It commences in the upper third posteriorly, and is directed 

 downwards and forwards on to the external surface, where it ter- 

 minates a little below and behind the apex of the deltoid impression. 

 The lower part of this groove is occupied by a pointed slip of the 

 brachialis anticus. In the upper part of the groove there is usually 

 a nutrient foramen for a branch of the superior profunda artery. 

 On the posterior aspect of the shaft, over about its upper third, 

 external to the spiral groove, there is a rough marking which gives 

 origin to the external head of the triceps, extending as high as 

 the lower part of the insertion of the teres minor. The internal 

 head of the triceps commences to arise in a pointed manner from the 

 back of the shaft internal to the spiral groove, where it reaches a 

 little above and behind the lower border of the tendon of the teres 

 major. 



The lower half of the shaft, being triangular, presents three 

 surfaces and three borders. The posterior surface, which is flat, 

 terminates at the olecranon fossa, and it gives origin to most of 

 the fibres of the internal head of the triceps. The external and 

 internal surfaces, as well as the anterior border which separates 

 them, give origin to the brachialis anticus. The anterior border, 

 which is round, separates the lateral surfaces, and is in line with the 

 anterior margin of the deltoid impression, and, above this, with the 

 outer bicipitcJ ridge. The external border is called the external supra- 

 condylar ridge. It is sharp and prominent, and extends from the 

 external epicondyle to the spiral groove. It gives attachment to 

 the external intermuscular septum. Anteriorly its upper two-thirds 

 give origin to the brachio-radialis (supinator radii longus), and the 

 lower third to the extensor carpi radialis longior. Posteriorly it 

 gives origin to the inner head of the triceps. The internal border 

 forms the internal supracondylar ridge, and is not so prominent as 

 the external. It commences at the internal epicondyle, and it can 

 be followed up through the line for the insertion of the coraco- 

 brachialis into the inner bicipital ridge. It gives attachment to 

 the internal intermuscular septum. Anteriorly it gives origin to the 

 brachialis anticus, posteriorly to the inner head of the triceps, and 

 "in its lower part to some fibres of the superficial head of the pronator 

 radii teres. The internal surface of the shaft, in front of the internal 

 supracondylar ridge and about 2| inches above the internal epicon- 

 dyle, sometimes presents a sharp spur-like projection directed down- 

 wards, called the supracondylar process. When present it gives 

 attachment to a fibrous band which passes to the internal epicon- 

 dyle, and gives origin to a third head of the pronator radii teres. 

 In such cases the band forms an arch through which the median 

 nerve passes, and frequently the brachial artery. The supra- 

 condylar process represents a portion of bone which forms a supra- 

 condylar foramen in many carnivora — e.g., the felidce. 



The lower extremity presents at either side the internal and ex- 

 ternal epicondyles, and interiorly a transversely elongated articular 



