Part 95

6. The stylohyoid (p. 112, and Fig. 65, d). Transect.

7. The digastric (p. 107, and Fig. 65, b). Transect, and reflect completely, to the origin and insertion.

8. The mylohyoid (p. 114, and Fig. 65, c). Transect and reflect.

9. The geniohyoid (p. 113, and Fig. 67, g).

10. The jugulohyoid (p. 113, and Fig. 67, b).

(The extrinsic muscles of the tongue (p. 228, and Figs. 67 and 96) may be dissected at this point, if desired. (a) The styloglossus; (b) the genioglossus; (c) the hyoglossus. They need not be cut.)

11. The masseter (p. 108, and Fig. 65, a). Cut the superficial and middle layers near their insertions by incisions parallel to the border of the jaw. Cut the deep layer near its origin. Look for the origin of fibres of the temporal muscle from the inner surface of the middle layer.

12. The temporal (p. 110, and Fig. 63, n). Clear its outer surface completely. Cut the temporal fascia transversely and reflect it toward the insertion of the muscle, with the superficial portion of the muscle. Cut through the zygomatic arch at its two ends and remove it, dissecting the fibres of the temporal free from their origin on its inner surface. Then examine the insertion of the temporal.

(The muscles of the pharynx (p. 232) may be dissected at this point; for directions, see page 451.)

13. The ceratohyoid (p. 115). To uncover this, the middle constrictor of the pharynx (Fig. 67, j) must be cut and reflected.

Cut the mylohyoid, geniohyoid, genioglossus, and the mucosa of the floor of the mouth free from the mandible on both sides, so that the tongue and the floor of the mouth may be drawn ventrad and turned out of the way, exposing the roof of the mouth (as in Fig. 66, p. 112). Cut through one side of the pharynx near the ventral surface and turn the tongue toward the uncut side.

The roof of the mouth is thus exposed. Dissect next--

14. The pterygoid muscles (Fig. 66). Remove the mucosa of the roof of the mouth, especially at the sides of the soft palate, and the two pterygoid muscles (p. 111) are exposed. The lower jaw may be removed on one side to get at their origin.

(The muscles of the soft palate (p. 230, and Fig. 66, d and e), and the superior constrictor of the pharynx (p. 233, and Fig. 66, f) may be observed at this point, if desired.)

V. MUSCLES OF THE WALL OF THE THORAX AND OF THE ABDOMEN.

1. The scalenus (p. 141, and Fig. 73, f-f‴). To trace its cervical portion, cut the trachea and œsophagus just craniad of the first rib, cut the pharynx and hyoid free from the ventral side of the head and neck, and remove the pharynx, larynx, œsophagus, and trachea (these should be preserved for future study of the larynx).

2. The transversus costarum (p. 150, and Fig. 73, j).

3. The serratus posterior superior (p. 148, and Fig. 73, l). Transect this at about the middle of the muscle-bundles, and reflect it in both directions.

4. The serratus posterior inferior (p. 148, and Fig. 73, n). Transect and reflect as in the last.

5. The external oblique (p. 153, and Fig. 68, p). Transect it by an incision parallel to its tendon of origin and about an inch from it, and reflect in both directions.

6. The internal oblique (p. 154, and Fig. 73, o). Transect and reflect as above.

7. The transversus (p. 155, and Fig. 69, l). Requires no further dissection.

8. The rectus abdominis (p. 155, and Fig. 73, k). Open its sheath by a longitudinal incision near the linea alba.

9. The external intercostals (p. 150, and Fig. 73, m; Fig. 69, i). To see these, remove the origins of the levator scapulæ and serratus anterior; also the serratus posterior superior.

10. The internal intercostals (p. 151, and Fig. 69, k). To uncover these, remove the external intercostals from between two or three pairs of ribs.

11. The transversus thoracis (p. 151). To see this muscle, which lies on the inner surface of the thoracic wall, it is necessary to cut through the ribs on one side one or two inches from the sternum, and open the thorax. The muscle can then be observed directly.

(The levatores costarum will be dissected later.)

VI. MUSCLES ON THE VENTRAL SIDE OF THE VERTEBRAL COLUMN IN THE NECK REGION (Fig. 72).