douthitt: supraglenoid canal. 263 



In Crotaphytus (Fig. 1) the two subclavians come off from 

 near the lower end of the right aorta by a single stem. After 

 about 1 mm. this common stem divides, and the two sub- 

 claviae pass directly laterad to the arm. At the point of their 

 separation, in the median line of the body, the vertebral artery 

 is given off as a single vessel. It runs directly forward on the 

 ventral surface of the centrum for about 2 mm. and then di- 

 vides into right and left vertebral arteries. 



The costocervical axis leaves the subclavian just laterad of 

 the centrum, and sinks at once into the muscles of the back. 



Beyond the costocervical, the subclavian passes beneath the 

 heavy longus colli muscle. Beneath the outer portion of this 

 muscle it gives off two or three small branches which pass to 

 the adjacent anterior regions. These should represent the 

 thyrocervical axis. A little further laterad another vessel 

 leaving the subclavian on the posterior side is no doubt the in- 

 ternal mammary artery. 



The axillary artery divides almost immediately. The brach- 

 ial continues down the arm in the usual manner. The lateral 

 branch, which is without doubt the subscapularis, passes to- 

 wards the space between the latissimus dorsi and a muscle 

 which corresponds in position and relations to the tey^es. The 

 subscapularis divides almost at once. The most posterior 

 branch divides soon into three branches, which spread over the 

 surface of the last-named muscle. The other branch turns to- 

 wards the axis of the limb, over the proximal portion of the 

 long head of the triceps, and into the space between this muscle 

 and the humerus. Here it divides into several branches, one 

 of which passes through the canal in question, to supply the 

 subscapularis muscle. 



There can be no reasonable doubt but that the supraglenoid 

 foramen and canal in all forms in which it occurs, has the same 

 function as the lizard ; that is, that it serves as a passage for a 

 branch of the subscapularis muscle. In mammals the sub- 

 scapularis artery proper passes laterad of the scapula and its 

 muscles, while only a minor branch passes to the subscapularis 

 muscle. In the lizard, however, this branch seems to be the 

 most important one. 



