DORSAL DIVISION OF SPINAL NERVES. 377 



primary division of the 2d cervical. Use the scalpel and tracer to 

 remove the muscles. After the ganglion is exposed, the neural 

 arch may be removed as usual with nippers. 



The removal of the 1st or suboccipital also requires care, as it 

 traverses the atlantal foramen. The muscles must be carefully 

 removed from the dorsal side of the atlas, commencing caudad. 

 The ganglion of this nerve is either in the muscles immediately cov- 

 ering the Fm. atlantale (§ 474) or just within the mouth of the fora- 

 men ; hence the muscles must be very carefully removed until the 

 nerve is uncovered. It may then be traced peripherad as far as 

 desired, and the dorsal part of the atlas removed with nippers. 



If it be desired to follow the brachial plexus as shown in Fig. 

 104, the rJiomhoideus and trapezius muscles must be removed (Fig. 

 66, 67), and also part of the serratus magnus (Fig. 73). Then the 

 scapula should be strongly lateriducted. This will expose the 

 hracMal plexus and its anastomoses, and the final trunks may be 

 made out by carefully dissecting with the tracer, fine forceps and 

 fine scissors. The 1st thoracic will be seen to pass entad of the 1st 

 rib on its way to join the brachial plexus. 



The distribution of the N. accessorius (xi) may be easily found, 

 as it extends along the ental surface of the M. trapezius, reaching 

 this point soon after its emergence from the Fm. jugulare in com- 

 pany with the NN. vagus et glossopTiaryngeus ; see § 562. 



§ 1012. Demonstration of the Dorsal {Posterior) Primary Division of the Nerties on the 

 Bight Side (Fig. 104). — In removing tbe skin from the right side, it should be torn rather 

 than cut : then the branches of the dorsal primary division going to the skin will be seen 

 as white cords which penetrate the muscles in the dorsal region and pass to the skin. 

 These branches should be followed through the muscles, using tracer, scissors, scalpel 

 and forceps as is necessary. Trace the dorsal division until it joins the ventral division 

 (Fig. 109). After the nerves are isolated, the right side of the neural arch should be 

 removed to the level of the intervertebral foramina. After the myelonal nerves are iso- 

 lated and the myelon uncovered, some cotton wet with 15 per cent, glycerin should he 

 placed upon the myelon and damp towels over the whole dorsal region, to protect the 

 parts from injury or drying. 



§ 1013. Exposure of the Brain.— The 12th, 11th, 10th, 9th and 

 7th cranial nerves (PL I, II), on the left side should be isolated. In 

 doing this, have at hand a skull and Fig. 56, 57, 59 and 107, also the 

 Table in § 562. If the structures are carefully removed opposite the 

 points of exit of the various nerves, they may be easily found and 

 traced as far peripherad as desired. After the nerves are isolated, 

 the roof of the skull should be removed with nippers. In doing 



