218 THE INFERIOR EXTREMITY 



nerve cells in the spinal medulla to the fibres of the muscles ; 

 they carry motor impulses to the muscles. Each posterior 

 root consists of nerve fibres passing to and from the nerve 

 cells in the ganglion of the root. The fibres of the posterior 

 root convey sensory impulses pain, heat, cold, etc. The 

 sensory impulses pass through the nerve cells of the ganglion 

 and then onwards to the spinal medulla. The trunk of 

 every spinal nerve, therefore, contains both motor and sensory 

 nerve fibres, and the posterior and anterior rami into which 

 it divides also contain both motor and sensory fibres. The 

 branches of the rami may contain both motor and sensory rami 

 or one or the other only ; eventually, however, the peripheral 

 parts of the fibres conveying impulses from the spinal medulla 

 and those conveying impulses to the spinal medulla separate 

 from one another. Every nerve consists of one or more fibres. 

 The fibres which convey impulses from the spinal medulla 

 become the motor nerves which end in muscle fibres, whilst 

 the fibres which convey impulses to the spinal medulla are 

 the sensory nerves, and those sensory nerves which carry 

 impulses from the skin are called cutaneous nerves. 



THE THIGH. 



On the morning of the fourth day after the subject has 

 been brought into the dissecting room, it is placed upon the 

 table lying upon its back ; the pelvis is supported by two 

 blocks, and the inferior extremities are stretched out at full 

 length. In this position it is allowed to remain for five days, 

 and during that period the dissector of the inferior extremity 

 has a very extensive dissection to perform. He has to dissect 

 (i) the anterior region of the thigh, including the trigonum 

 femorale and its contents, (2) the medial region of the thigh, in- 

 cluding the adductor canal and its contents. With so much 

 work to be completed, within a limited time, he must appor- 

 tion the five days to the best advantage. During the first day 

 he should dissect the superficial structures of the whole of the 

 anterior and medial aspects of the thigh. During the second 

 and third days he should complete the dissection of the 

 femoral triangle and the anterior region of the thigh, and the 

 remainder of the period should be devoted to the dissec- 

 tion of the medial region. 



Surface Anatomy. Before making the preliminary incisions 



