398 PRACTICAL ANATOMY. 



all supply the skin of the back ; there are twelve dorsal cutaneous nerves ; the 

 suboccipital is the first cervical posterior division ; the great occipital is the 

 posterior division of the second cervical ; the third occipital is a branch of the 

 third cervical, posterior division. 



You will find the (i) suboccipital nerve in the suboccipital triangle ; (2) the 

 great occipital under the complexus muscle crossing the suboccipital triangle ; 



(3) the spinal accessory nerve between the trapezius and sterno-mastoid muscles ; 



(4) the third occipital internal to the great occipital ; (5) the suboccipital emerges 

 between the occipital bone and atlas behind the vertebral artery ; (6) the great 

 occipital nerve emerges between the atlas and axis and passes under cover of the 

 complexus muscle through the lower and inner part of the suboccipital triangle ; 

 (7) the great occipital nerve joins the occipital artery under the trapezius and 

 lies on the complexus muscle ; (8) other posterior divisions emerge between the 

 transverse processes. 



Arteries of the back are: (i) the dorsal branches of all the intercostals ; 

 (2) the deep cervical, a branch of the superior intercostal ; (3) the arteria prin- 

 ceps cervicis, a branch of the occipital ; (4) these arteries, represented by num- 

 bers 2 and 3, anastomose under the complexus. 



The student who studies in advance of his dissection the foregoing pages 

 will have no difficulty in making a thorough dissection of the back. 



Dissection. Locate : (i) The spinous processes of the vertebra in the dorsal 

 and lumbar regions ; (2) the iliac crest ; (3) the crest of the scapular spine ; (4) 

 the three lips of the crest of the scapular spine ; (5) the acromion process of the 

 scapula ; (6) the external occipital protuberance ; (7) the vertebra projiiinens ; 

 (8) the angles of the ribs, and note the distance they are from the spinous 

 processes; (9) the iliac junction with the sacrum ; (10) the rudimentary sacral 

 spines ; (i i) the inastoid processes ; (12) the clavicle ; (13) the twelfth rib. 



Incisions. (i) From external occipital protuberance to the rudimentary 

 sacral spines ; (2) from one acromion process of the scapula to the other. Begin 

 to remove the skin at the intersectional point of the vertical and horizontal inci- 

 sions just made. 



Observe the cutaneous nerves piercing the trapezius and latissimus dorsi, on 

 removing the skin. These are the cutaneous branches of the posterior divisions 

 of the spinal nerves. (Fig. 279.) 



Note the very heavy variety of the superficial fascia. This, you will 

 observe, is tightly bound to the deep fascia by fibrous trabeculae that make 

 removal of the skin difficult. This fascia, especially in the region of the neck, 

 is a common place for boils and carbuncles. Observe the great depth you will 

 have to cut to get through this fascia. 



Clean all the superficial fascia off and make your work look like figure 227. 

 Here you have exposed two muscles : (i) The trapezius ; (2) the latissimus clorsi. 



The Trapezius. Trace its origin to the external occipital protuberance, the 

 inner third of the superior nuchal line, the ligamentum nuchae, the seventh cer- 

 vical spine, and all the dorsal spines. Now pull the arm outward (Fig. 280), and 

 put the muscle on the stretch. Study its descending fibres to the outer third of 

 the clavicle and acromion ; its ascending and horizontal ones to the upper lip of 

 the spine of the scapula. 



Develop the lower margin of the trapezius muscle, and observe that it overlaps 

 the latissimus dorsi. Find the space between the trapezius and sterno-cleido-tnas- 

 toid muscle. Locate in this space the spinal accessory nerve, and trace the 



