Dissection of Common Rat. 195 



outwards ; next, let the Pectoralis major be detached by- 

 dividing the muscle along its attachment to the Clavicle (but 

 being very careful not to injure the injected jugular vein 

 which will be seen to pass superficial to the" Clavicle) and by- 

 making a vertical incision through its substance a little ex- 

 ternal to its line of attachment to the sternum and costal 

 cartilages. This muscle should then be reflected outwards, 

 and its tendon, attached to the Humerus, carefully examined. 

 By this means the Pectoralis minor, situated at the upper part 

 of the Thorax immediately beneath the Pectoralis major, will 

 be exposed, arising from near the cartilages of the anterior 

 ribs, and inserted into the Coracoid process of the Scapula. 

 The costal attachment of the Pectoralis minor should be 

 divided across, and the muscle reflected outwards, by which 

 means the axillary vessels and nerves are brought fully into 

 view, and should be next examined. 



In the Axilhy or space between the upper and lateral parts 

 of the chest, and inner side of the arm, are contained 

 the axillary vessels and the brachial plexus, with their 

 branches. This cavity is filled with a good deal of areolar 

 tissue, which must be carefully removed, and the vessels and 

 nerves cleaned from the clavicle to the elbow. The chief 

 vessel crossing the outer portion of the space is the axillary 

 vein ; close to this is the (white) median nerve, and just in- 

 ternal to these is the axillary artery ; the axillary vein always 

 being on the Thoracic side of the artery, and of greater 

 calibre. The Biceps muscle, which extends from the Scapula 

 to the Radius, fills up the rest of the outer space. A bristle 

 should, be passed up the artery for further investigation later 

 on. The axillary vein bringing the blood up from the fingers 

 terminates about a quarter of an inch posteriorly to the 

 Clavicle, and becomes the subclavian vein. The axillarij artery 

 is the continuation of the subclavian artery, which comes from 

 the Arteria innominata on the right side ; but direct from the 



