Part 96

Clean the surface of these muscles, removing pharynx, larynx, œsophagus, and trachea, if this has not been done.

1. Longus capitis (p. 142, and Fig. 72, a).

2. Longus colli (p. 144, and Fig. 72, g′, g″).

3. Levator scapulæ ventralis (p. 120, and Fig. 72, c′, c″). Observe its origin.

4. Rectus capitis anterior minor (p. 143, and Fig. 72, b). To see this, cut through on one side the longus capitis and one head of the levator scapulæ ventralis, and remove the proximal portions, as in Fig. 72.

5. Obliquus capitis superior (p. 136, and Fig. 72, e).

6. Rectus capitis lateralis (p. 143, and Fig. 72, d).

VII. MUSCLES OF THE BACK (p. 123).

Remove what remains of the dorsal portion of the latissimus dorsi, serratus posterior superior, and serratus posterior inferior. See that the skin is removed completely to the dorsal middle line, or even for a little distance over onto the other side. There is thus exposed the lumbodorsal fascia (p. 126), covering the muscles of the back.

Cut the superficial layer of the lumbodorsal fascia (that from which the latissimus dorsi and obliquus externus abdominis have origin) by an incision parallel to the dorsal median line, and remove it. The muscles of the back are thus exposed (Fig. 69). Observe in the lumbar region the longissimus dorsi (f, f′, f″); in the thoracic region the longissimus dorsi, the spinalis dorsi (g), and the iliocostal (h); in the cervical region the splenius (Fig. 73, b).

1. The longissimus dorsi (p. 126, and Fig. 69, f, f′, f″). Notice in the lumbar region the strong deep layer of the lumbodorsal fascia, by which this muscle is covered, and from the under side of which many of the fibres of the muscle take origin. Cut this fascia by an incision parallel to the dorsal median line and about two centimeters from it, from the level of the crest of the ilium as far craniad as the fascia can be cut without cutting into the muscle-fibres (usually to about the level of the last rib). Reflect the medial division of the fascia to the middle line. Reflect the lateral division of the fascia until it passes into the muscle and cannot be farther reflected.

Observe then in the lumbar region the medial (Fig. 70, a) and lateral (Fig. 70, b) divisions of the longissimus dorsi, and the portion (b′) of the lateral division taking origin from the lumbodorsal fascia (c). Dissect apart some of the muscle-fibres of the longissimus and observe their origin and insertion.

Trace the longissimus dorsi into the thoracic and cervical regions (Fig. 69, f′, f″) noting the separation off from it on the dorsal side of the spinalis dorsi (Fig. 69, g); on the ventral side of the iliocostal (Fig. 69, h).

2. The extensor caudæ lateralis (p. 137, and Fig. 70, f). Uncover this by cutting the lumbodorsal fascia over the sacral region.

3. The iliocostalis (p. 128, and Fig. 69, h). Uncover this completely; note its connection with the longissimus dorsi at the caudal end. Dissect apart some of its muscle-bundles, to see origin and insertion.

4. The splenius (p. 131, and Fig. 73, b). Transect this by an incision beginning at its lateral border about four centimeters from the cranial end of the muscle and extending obliquely craniodorsad to the craniomedial angle of the muscle. Be careful not to injure the longissimus capitis (Fig. 73, g).

5. The longissimus capitis (p. 131, and Fig. 73, g). Transect.

6. The spinalis dorsi (p. 129, and Fig. 69, g). Separate some of its muscle-fibre bundles and trace to origin and insertion.

7. The biventer cervicis (p. 132, and Fig. 69, a). Raise its lateral border, turning it toward the middle line, and transect it near its caudal end.

8. The complexus (p. 133, and Fig. 69, b). Raise its medial border, and transect it near its cranial end.

9. The longus atlantis (p. 134, and Fig. 71, f).

10. The multifidus spinæ (p. 130, and Fig. 70, d). Remove a part of the longissimus dorsi in the lumbar region, and trace the course of the fibres of the multifidus spinæ. (If desired the entire longissimus may be removed and the multifidus spinæ completely uncovered.)

11. The extensor caudæ medialis (p. 136, and Fig. 70, e).

12. The semispinalis cervicis (p. 133, and Fig. 71, c). Dissect apart some of its fibre-bundles to see origin and insertion.

13. The interspinales and intertransversarii (p. 131) may be seen in the region from which the longissimus dorsi was removed, by removing the bundles of the multifidus spinæ.

14. The rectus capitis posterior major (p. 134, and Fig. 71, a). Transect.

15. The obliquus superior (p. 136, and Fig. 71, e).

16. The obliquus capitis inferior (p. 136, and Fig. 71, b).