DORSAL REGION. PECTORAL REGION. 1061 



semispinalis dorsi and colli muscles may then be examined. Lastly, the 

 deepest muscles, multifidus spinne, rotatores spinse, interspinales, and inter- 

 trans versales are to be dissected (p. 238). 



At this stage of the dissection a good view may be obtained of the 

 posterior margins of the obliquus externus and obliquus internus muscles of 

 the abdomen, and of the posterior and middle layers of the lumbar aponeu- 

 rosis, which are continuous behind with the trans versalia muscle : the 

 dissection of these muscles, however, belongs to the abdomen, and they 

 must not be injured (p. 199). 



The next proceeding for a senior dissector is to lay bare the spinal cord ; 

 for this purpose he will straighten as much as possible the lumbar vertebrae, 

 by placing blocks underneath the abdomen, and will let the neck hang 

 slightly downwards. He will then saw through the laminae of the dorsal 

 and lumbar vertebra on each side, keeping the edge of the saw directed 

 slightly inwards, and will continue the saw-cuts below on the back of the 

 sacrum, so as to meet each other where the sacral canal becomes incomplete. 

 The part so isolated may easily be raised with the chisel, and with the bone- 

 nippers the whole laminae of the vertebrae may be removed, attached to one 

 another by their elastic ligaments. In several spaces of the lower dorsal 

 region the articular processes of the vertebrae may be removed, so as to 

 expose one or more of the spinal nerves issuing from the canal, and these, 

 being dissected for a little distance beyond their ganglia, may be afterwards 

 taken out along with the cord. The theca of dura mater ought now to be 

 made as clean as possible by removing the fat from its surface, and, after 

 being examined, should be slit open, that the other membranes and the 

 relations of the cord may be examined in situ ; more particularly, the 

 ligamentum deuticulatum, the position of the lower extremity of the cord, 

 the cauda equina, and the filum terminale will be observed (pp. 502 and 

 565). The spinal cord and its membranes are then to be removed from 

 the body and stretched out upon a table, when the anterior and posterior 

 roots of the nerves and some of the ganglia in connection with the latter 

 may be observed ; also the external form and structure of the cord, with 

 the anterior, middle, and posterior columns, the anterior and posterior 

 fissure, <fec. ; and, lastly, several sections of the cord, in different places, 

 may be made to exhibit the relations of the grey and white matter within. 



2. Pectoral Region and Axilla. Within four days after the subject has 

 been laid upon its back, the pectoral region and the axilla are to be dis- 

 sected. Let a median incision be made in front of the sternum, and from 

 its upper end let another be carried along the clavicle to the acromion, and 

 thence downwards to the inside of the middle line of the arm, a little 

 below the fold of the axilla, and a third horizontally outwards from the 

 lower end of the sternum. Then let the skin be reflected from the 

 pectoralis major muscle (p. 203), and let the senior student in doing this 

 preserve the fibres of the platysma myoides and the suprasternal and supra- 

 clavicular branches of the cervical plexus of nerves descending over the 

 clavicle (pp. 170 and 639), the anterior cutaneous branches of the inter- 

 costal nerves, with the accompanying twigs from the internal mammary 

 artery near the middle line, and two or three small anterior twigs of the 

 lateral cutaneous branches of the intercostal nerves appearing round the 

 lower border of the muscle (pp. 656 and 375). If the subject be a 

 female, let him also dissect the mammary gland, and in raising the general 

 integument leave the skin of the nipple, by carrying round it a circular 

 incision of about two inches in diameter (p. 1002). By raising the skin 



