376 ANATOMICAL TUCHNOLOOT. 



Choice of Spedmen. — A lean cat with milk teeth is preferable : ymmg, because the 

 bones are softer and more easily cut ; lean, because the tracing of nerves is difficult even 

 when unobscured by fat. The usual precautions for cleanliness should be observed (g 199), 

 and if it be desired to demonstrate the iiertebral artery as in Fig. 104, the arteries should 

 be injected from the abdominal aorta or the femoral artery ^§§ 845, 363). The cat should 

 be deprived of blood by opening the V. femoralis near Poupart's ligament, centrad of the 

 last pair of valves (§ 362), or the postcava may be opened. 



Posture. — Place the cat ventricumbent with a block between the 

 arms and under the neck, so that the structures on the dorsal part 

 of the body may be somewhat tense. The legs should be tied to 

 the tray, so that the subject will not move too much. 



§ 1010. Exposure and Dissection. — Part the hair (§ 354) along 

 a line 1 cm. sinistrad of the dorsimeson, commencing at the base of 

 the skull and ending opposite the gleno- vertebral angle of the scap- 

 ula. Cut the skin along this line and reflect it for 2-3 cm. on the 

 left and just beyond the dorsimeson on the right. In reflecting the 

 skin on the right, it should be torn from the body rather than cut, 

 so that the nerves passing into the skin may be more easily de- 

 tected. During the dissection the parts should be kept covered 

 with skin as much as possible and moistened occasionally with 15 per 

 cent, glycerin. In case it takes more than one day to complete the 

 study, the preparation should be moistened with 15 per cent, gly- 

 cerin, covered with skin and then with a damp towel, and kept in a 

 cool place. As the dissection of a given part is completed, there 

 should be laid upon it a tuft of cotton moistened with 15 per cent, 

 glycerin. 



§ 1011. Demonstration of the Ventral Primaxy Division of 

 Nerves of the Left Side (Fig. 104). — After the skin is reflected on 

 the left side, commence in the 7th intervertebral space and cut the 

 muscles from the left half of the neural arch (§ 478), and with the 

 tracer carefully isolate the nerve as it emerges through the interver- 

 tebral foramen (§ 484). Then with the nippers remove the left half 

 of the neural arch, and the origin of the nerve from the myelon wiU 

 be seen. Continue to expose the nerves in this way until the 2d 

 cervical or great occipital nerve is reached. This does not emerge 

 through a special intervertebral foramen, but between the arches of 

 the atlas and axis ; hence the ganglion is imbedded in the muscles. 

 It is most safely isolated by tracing it from the surface toward its 

 origin. This nerve is easily seen on the caudal part of the head and 

 through the clavo-trapezius muscle if the cat is lean. One might 

 also begin with the N. auricularis magnus (Fig. 87) the ventral 



