38 THE UPPER EXTREMITY 



should comprise (i) the reflection of the skin; (2) the 

 dissection of the cutaneous nerves and vessels; and (3) the 

 cleaning of the latissimus dorsi and trapezius muscles. The 

 remainder of the dissection can be undertaken on the second 

 day. 



Reflection of the Skin. The following incisions are necessary: i. 

 From the tip of the coccyx upwards, along the middle line of the body, 

 to the spine of the seventh cervical vertebra. 2. From the upper end of 

 the foregoing medial incision transversely, to the tip of the acromion 

 of the scapula. 3. From the lower extremity of the median incision 

 in a curved direction laterally and forwards, along the crest of the 

 ilium, to within two inches of the anterior superior iliac spine. 4. An 

 oblique incision from the spine of the first lumbar vertebra, upwards 

 and laterally, to the posterior fold of the axilla, and along the latter to 

 the arm. The two large flaps which are now mapped out upon the back 

 must be carefully raised from the subjacent fatty tissue. Reflect the upper 

 triangular flap first, and then the lower flap. 



Panniculus Adiposus (Superficial Fascia). In subjects 

 which have been allowed to lie for some time on the back 

 the superficial fascia is usually more or less infiltrated with 

 fluid which has gravitated into its meshes, otherwise it has 

 the ordinary characters of superficial fascia (p. 5). 



Dissection. In searching for the cutaneous nerves cut boldly down 

 through the superficial fascia, in the direction in which the nerves run 

 (Fig. 17), until the plane is reached at which the superficial and deep fascia 

 blend. It is here that the main trunks are to be found and in a well 

 injected subject the cutaneous arteries will serve as guides. A more rapid 

 way of finding the cutaneous nerves in this region is to reflect the superficial 

 and deep fascia laterally from the vertebral spines in one layer ; the nerves 

 are then found as they issue from the muscles. This plan, however, should 

 only be adopted by the senior student. 



Vasa Cutanea, Nervi Cutanei (Cutaneous Vessels and 

 Nerves). The cutaneous nerves of the back are derived from 

 the posterior branches of the spinal nerves. As the posterior 

 branches pass backwards, they subdivide into medial and 

 lateral divisions. Both of these supply twigs to the muscles 

 amongst which they lie ; but one or the other also contains 

 some sensory fibres which come to the surface, in the shape 

 of a cutaneous nerve, to supply the skin. 



In the thoracic region the upper six or seven cutaneous 

 nerves are the terminations of the medial branches of the 

 posterior rami of the thoracic nerves. They become super- 

 ficial close to the vertebral spines, and are to be sought 

 for near the median plane. It is not uncommon to find one 

 or more of them piercing the trapezius one or two inches 



