66 OUTLINES OF EQUIXE ANATOMY. 



beliiud tlie ridge is a tria,ugular roiigliened space extending 

 to tlie fonrtli tubercle. To the anterior part of this the in- 

 ferior extremity of scapnlo-humeralis externus is attached, 

 while its inferior margin marks out the limit of humeralis 

 externus and the line of attachment of caput medium of 

 triceps extensor brachii. The foiirth tuhercle, situated ex- 

 ternally to the head, is continuous with the antero- external 

 tubercle. It has the articulatory surface for the scapula 

 extending on to its internal surface, while its external sur- 

 face affords attachment to one head of postea spinatus, over, 

 which the other head plays, with a bursa intervening, to 

 become inserted into the upper part of the ridge. Just 

 below the fourth tubercle is a row of articulatory foramina. 

 The shaft of this bone presents four surfaces ; the internal 

 is straight ; superiorly, just below the roughened surface 

 for attachment of subscapularis, the upper head of coraco- 

 humeralis becomes attached. Centrally, at the superior 

 part of the middle third, elongated from above downwards, 

 is a roughened ovoid space for insertion of the common 

 tendon of teres internus and latissimus dorsi. Below this, 

 inclined to the anterior surface, is the attachment of the 

 lower head of coraco-humeralis ; between the two heads 

 runs a branch of the humeral artery with its satellite vein 

 and nerve to flexor brachii, from behind forwards, but the 

 attachment of teres internus is a little posteriorly placed 

 to their connecting line. Straight down the limb, but in 

 consequence of the position of the bone, oblicjuely over its 

 inner surface, the humeral artery runs from the inner sur- 

 face of the shoulder-joint downwards to the inner part of 

 the elbow-joint. At the superior part of the inferior third 

 of the bone it gives off the medullary artery, which pierces 

 the medullary foramen here situated. The goiTesponding 

 vein is more posteriorly placed. The anterior surface is 

 superiorly smooth, mainly occupied by flexor brachii run- 

 ning downwards, slightly inclined inwards, after passing 

 over the tubercles of the humerus. The roughened attach- 

 ment of the long head of coraco-humeralis encroaches 

 upon this surface at the superior part of the inferior third, 

 and is separated by a prominent line running downwards 

 from the ridge on the external surface, from a deep de- 

 pression just above the lower articulatory surface which 

 almost (in some species of animals quite) extends through 

 the bone as far as the supra- condyloid fossa. This is the 



