DEEP DISSECTION OF THE BACK. 519 



Fallopii to join the facial nerve. External to this is sometimes 

 seen the small superficial petrosal nerve (tig. 240, 3 ), but this is 

 frequently concealed in the substance of the temporal bone. The 

 source and destination of these small nerves will be afterwards 

 learnt. It will suffice now for the student to notice their position, 

 and to see that they are kept moist and fit for examination at a 

 future time. 



Directions. When the study of the base of the skull has been Directions 

 completed a preservative fluid should be applied, and the flaps 

 of skin should be stitched together over all. 



SECTION III. 



DEEP DISSECTION OF THE BACK. 



Directions. During the first two days that the body is placed on Directions, 

 its face the dissector of the head and neck should be careful not to 

 let his work interfere with that of the worker on the upper limb, 

 whose duty it is in this time to dissect the superficial structures 

 below the level of the seventh cervical spine, and to study and 

 reflect the first two layers of the muscles of the back, and to 

 examine the related structures as described in pages 1 to 10. The 

 dissector of the abdomen also should have the opportunity of 

 examining the arrangement of the fascia lumborum when it is 

 displayed on the third day. 



Position. The body lies with the face downwards ; and the Position of 

 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 six successive layers of muscles, amongst strata in 

 which vessels and nerves are interspersed. The student should ac ' 

 go over again the surface anatomy of the back, as described on 

 > 2. 



Dissection. Make an incision along the middle line of the To raise the 

 neck from the external occipital protuberance to the spine of the s 1D ' 

 seventh cervical vertebra, and reflect the skin outwards as far as 

 the mastoid process above and as far as the outer border of the 

 acromion below. 



On the first day the cutaneous branches of the posterior divisions Clean 

 of the cervical nerves should be displayed, the trapezius muscle 

 cleaned in the neck, and the small occipital nerve traced down 

 from the scalp in its tube of fascia along the posterior border of 

 the sterno-mastoid muscle. 



To find the nerves in the cervical region, look near the middle 

 line, from the 3rd to the 6th vertebra, trace an offset from the 

 third nerve upwards to the head, and follow the great occipital 

 nerve down from the scalp to its emergence from the muscles. 



