110 ANATOMY OF UPPER EXTREMITY, ETC. 



nerves. This dissection will at least show the importance 

 of exploring the arm for the pulsations of the artery with 

 reference to its -relation to the vein, whichever it may be 

 that it is proposed to open, if the dangers of traumatic 

 aneurism would be avoided. 



In the dissection of the elbow, a lymphatic gland will be 

 found with a considerable degree of constancy, just above 

 the inner condyle; practically important, as being some- 

 times enlarged and inflamed from wounds or ulcerations of 

 the hands or fingers, and almost constantly so in cases of 

 constitutional syphilis. 



DISSECTION III. 



STERNAL REGION. 



The further dissection of the upper extremity is now to l>e relin- 

 quished until the thorax and its' contents have been examined. It 

 should be carefully wrapped in a bandage and kept constantly damp 

 until its dissection is resumed. 



The anterior wall of the thorax is to be removed by dividing upon 

 each side the costal cartilages and intercostal muscles, close to the 

 ribs. If the lungs be free from adhesions, and the pleural cavity has 

 not yet been opened, the student will hear, as he first opens into it, 

 the whistle of the air as it enters the vacuum previously existing, and 

 will see the lungs collapse under the atmospheric pressure to which 

 they are then first subjected. If the dissection of the muscles attached 

 to the upper part of the sternum and clavicle is completed, the whole 

 of the sternum may be removed ; otherwise a portion must be left by 

 sawing it across, an inch below its summit. The segment included in 

 the incisions made is to be lifted, first by one and afterward by both 

 of its lower angles, and the cellular and muscular tissues divided 

 which attach it to the parts beneath. Its separation at the first rib 

 and from the clavicle is a little difficult, unless properly performed ; 

 the knife, as it approaches the first rib, should be directed obliquely 

 outward till its cartilage is divided, then turning at right angles to 

 this incision, it is to be carried inward, gradually describing a curve 

 with its concavity outward, through the sterno-clavicular articulation. 

 Every autopsy which the student attends affords him opportunity of 

 studying nearly all the parts about to be described. 



Upon the inside of the plastron, as the segment thus 

 removed is called, beneath a layer of cellular tissue, will 

 be found a muscle called the TRIANGULARIS STERNI; it arises 

 from the sides of the sternum as high as the third cartilage, 

 from the ensiform cartilage, and sternal extremities of the 



