DISSECTION OF THE BACK. 353 



CHAPTER Y. 



DISSECTION OF THE BACK. 



Directions. The dissection of the Back may be undertaken by one stu- 

 dent ; or conjointly by the dissectors of the head and upper limbs the 

 former preparing the neck, and the latter making ready the parts in the 

 dorsal and lumbar regions. 



If the Back should be allotted to more than one student, the dissector 

 of the upper limb may attend chiefly to the paragraphs marked with an 

 asterisk ; and the dissector of the neck may study specially the paragraphs 

 which are not so marked. But as many of the dissections in the earlier 

 stages require the co-operation of the students employed on the same side 

 of the body, a general attention may be given to the whole by each. 



The dissector of the abdomen is to examine the arrangement of the fas- 

 cia lumborum, after the first layer of muscles has been learnt. 



Position. The body lies with the face downwards ; and the trunk is to 

 be raised by blocks beneath the chest and the pelvis, so that the limbs 

 may hang over the end and sides of the dissecting table. To make tense 

 the neck, the head is to be depressed and fastened with hooks. 



In this region there are five successive strata of muscles, amongst which 

 vessels and nerves are interspersed. 



Dissection. The first step is to raise the skin in two flaps, by means of 

 the following incisions : One cut is to be made along the middle of the 

 body from the occipital protuberance to the back of the sacrum. Another 

 is to be carried from the last dorsal vertebra to the acromion process of 

 the scapula. The flap of skin above the last cut is to be turned outwards 

 by the dissectors of the head and upper limb. 



By another transverse incision opposite the iliac crest, the remaining 

 piece of integument may be detached, and reflected by the dissector of the 

 upper limb in the same direction as the other flap. 



Under the upper flap of skin is placed the trapezius, and underneath the 

 lower one the latissimus dorsi muscle. 



The cutaneous nerves may now be sought in the superficial fatty layer : 

 they are accompanied by small cutaneous arteries which will guide the 

 student to their position. The nerves vary much in size in the different 

 parts of the Back, and their number is also irregular ; as a general rule, 

 there is one opposite each vertebra except in the neck. 



To find them in the cervical region look near the middle line, from the 

 3d to the 6th vertebra, and trace an offset from the third nerve upwards 

 to the head : the branch of the second nerve (large occipital) has been 

 laid bare at the back of the head (p. 20). 



Opposite the upper part of the thorax, they will be best found near the 

 spines of the vertebrae, where they lie at first beneath the fat; but at tin- 

 lower part, and in the loins, they issue in a line with the angles of the ribs. 



The cutaneous branches of the sacral nerves are included in the dissec- 

 tion of the lower limb. 

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