Part 39

The specimens should be kept in a tight box, that the fluid may not evaporate rapidly from the cloths used for wrapping.

The attacks of the mould present a difficulty not so easily overcome. As long as the specimens are in daily use for dissection, and exposed parts kept covered with cloths saturated with the glycerine and formalin mixture, little or no trouble is to be anticipated. But if the specimens are left untouched for some days, and particularly if exposed surfaces are not kept covered in the manner above recommended, mould is almost sure to attack them. Material neglected for a week may thus be ruined.

If mould is found at any time to be attacking the material, the attacked part should be cleaned and well wrapped in cloths saturated in the formalin-glycerine mixture. If such means are unavailing, the specimen should be immersed in a vessel of one per cent. formalin and preserved for the future in this. Recourse should be had at once also to this method of preservation if the specimen shows signs of decomposition by having a strong odor.

It seems probable that the attacks of the mould might be prevented by mixing some fungicide with the injecting fluid; experiments should be made in this direction.

There are many advantages in preserving the material if possible without immersing it. All parts retain their color and pliability much more completely, so that the different structures are much more easily distinguishable. The method above described, by the use of formalin and glycerine, is to be recommended when the material is to be worked on every day or so and is not to be kept longer than a few weeks. It is usually not very satisfactory in warm weather, however. If some method can be devised of entirely preventing the attacks of the mould, this will be an excellent method of preserving anatomical material.

The same specimens used for the study of the muscles will serve also for the spinal cord and brain if prepared by one of the methods above described. (For the viscera, blood-vessels, and nerves, other specimens will have to be prepared; for these, directions are given later.)

_Muscles to be Dissected._--It will probably usually be impossible in a given course of study to dissect all the muscles of the cat. The instructor will of course select such as seem most advisable to him. The following may perhaps be recommended as a good selection for a fairly extensive course: Muscles of the Fore Limbs (pp. 436-439); Muscles of the Neck and the Deep Muscles of the Head (pp. 439-441); Muscles of the Wall of the Thorax and of the Abdomen (pp. 441-442); Muscles on the Ventral Side of the Neck (p. 442). If the superficial facial muscles (excluding those of the ear) can be studied from a preparation, this will be a valuable addition to a course (pp. 434-435).

DISSECTION OF MUSCLES.

_General._--In dissecting muscles a prime requisite of successful dissection is to keep the muscles _clean_. Fat, connective tissue, etc., is to be carefully but thoroughly cleared away from the surface of muscles and from between them. Frequently when it seems impossible to distinguish the structures described, all difficulty will vanish as soon as the dissection is thoroughly cleaned.

In transecting a muscle, work under it completely from one edge to the other (except in case of very wide muscles), then introduce the scissors or scalpel, and cut it by a smooth clean cut. Always leave the entire origin with one-half of the muscle, the entire insertion with the other half.

The student must be prepared to find in some cases considerable variations from the conditions described. The descriptions attempt to give an account of the _usual_ structures, but specimens showing no variations whatever are undoubtedly rare.

DIRECTIONS FOR DISSECTING THE MUSCLES OF THE CAT.

I. THE SKIN-MUSCLES (pp. 93-96, and Fig. 62).

These will perhaps not usually be dissected. If they are to be dissected, proceed as follows: Make a ventral median longitudinal incision of the skin from the cranial end of the manubrium to a point opposite the crest of the ilium. Connect the cranial end of this incision with the middle of the lambdoidal ridge by a similar incision through the skin. Make another incision from the manubrium to the spinous process of the thirteenth thoracic vertebra. Connect the caudal end of the first incision by an oblique cut with the root of the tail. Make another incision from the convexity of the knee-joint along the fold of skin which connects the hind limb and body, as far as the incision which leads to the root of the tail. Make an incision surrounding the base of the forelimb. Now reflect these flaps one at a time, working in general from the ventral side toward the dorsal middle line. Take great pains not to take up the thin skin-muscle with the skin. In this way all of one side of the body will be uncovered. The cutaneus maximus (Fig. 62, _b_) and a part of the platysma (Fig. 62, _a_) will be thus exposed. Read and verify the descriptions of these muscles (pp. 93-96). The cranial portion of the platysma cannot be seen at this stage, but should be dissected in connection with the muscles of the face.

II. SUPERFICIAL MUSCLES OF THE FACE AND HEAD (pp. 96-107, and Figs. 63 and 64).

These will perhaps not usually be dissected by the student. They should be studied on a well-dissected laboratory preparation, if possible. If they are to be dissected, this should be done if possible on a fresh specimen, as it is very difficult to dissect them on preserved material. Proceed as follows:

The skin should be removed with care from the sides and top of the face and head, without injury to the external ear.

1. The platysma (p. 95, and Fig. 62, _a_). Determine its cranial attachments.

2. The intermedius scutulorum (p. 96, and Fig. 63, _a_).

3. The corrugator supercilii medialis (Fig. 63, _b_).

4. The orbicularis oculi (Fig. 63, _c_; Fig. 64, _s_).

5. The corrugator supercilii lateralis (Fig. 64, _k_).

6. Notice the frontoauricularis if it exists.

7. The levator auris longus (Fig. 63, _g_, _g′_). Transect and reflect.

8. The auricularis superior (Fig. 63, _k_). Transect.

9. The abductor auris longus (Fig. 63, _m_). Transect.

10. The abductor auris brevis (Fig. 63, _l_). Transect.

11. The epicranius (Fig. 63, _h_, _h′_). In dissecting this muscle the intermedius scutulorum and corrugator supercilii medialis may be cut by an incision parallel to the middle line but a short distance to one side of it.

12. The zygomaticus (Fig. 64, _d_). This and the two following muscles may usually be best seen running beneath the fibres of the platysma, without reflecting the latter. If necessary, however, the platysma may be transected and reflected, though this can be done only with great difficulty.

13. The submentalis (Fig. 64, _c_).

14. The depressor conchæ (Fig. 64, _b_).

The zygomaticus, submentalis, and depressor conchæ should now be transected one or two centimeters from the external ear. The corrugatores supercilii lateralis and medialis may be cut across between the eye and the ear, and reflected. There is thus exposed:

15. The frontoscutularis. Transect near the scutiform cartilage.

16. The adductor auris inferior (Fig. 64, _o_). Transect near its insertion.

The external ear is now attached to the head only by the external auditory meatus and the tragicus lateralis muscle. Read the description of the latter (p. 418, and Fig. 67, _a_), find it beneath the fat which surrounds the proximal portion of the external ear, and cut it as far ventrad as possible. Now cut across the cartilaginous auditory meatus as near to the tympanic bone as possible, and remove the external ear, preserving it for future study. (The remainder of the muscles of the external ear may be studied in connection with the study of the auditory organ.)

17. The orbicularis oris (p. 105 and Fig. 64, _i_).

18. The zygomaticus minor, if it exists (p. 105, and Fig. 64, _e_).

19. The quadratus labii superioris (p. 105).

_a._ The levator labii superioris proprius (Fig. 64, _f_).

_b._ The levator labii superioris alæque nasi (Fig. 64, _g_).

20. The caninus (p. 106, and Fig. 64, _f′_).

21. The buccinator (p. 106).

22. The myrtiformis (p. 106, and Fig. 64, _h_).

23. The “moustachier” (p. 107).

24. The quadratus labii inferioris (p. 107).

III. MUSCLES OF THE FORE LIMB.

A. _Muscles connecting the Arm with the Body._--If the skin-muscles have been dissected, as above, cut the cutaneus maximus near its insertion, and reflect it toward the median dorsal line; in this way remove it completely. Remove the platysma in the same way. The first layer of body-muscles is thus exposed.

If the skin-muscles are not to be dissected, these may be removed with the skin. If the skin has not yet been removed, proceed as follows:

Beginning at the cranial end of the manubrium make two incisions in the skin, one passing to the lambdoidal ridge and the other to the spinous process of the thirteenth thoracic vertebra. Raise the triangular flap thus formed, taking up the skin-muscles with it.

1. The trapezius group of muscles (pp. 115-117, and Fig. 68, _d_, _h_, and _j_) is now exposed and may be dissected. Begin with the spinotrapezius (Fig. 68, _j_). Read the description of the muscle, then raise its caudal border and work under it until its cranial border is reached and the middle of its inner surface is free. Then transect it, and reflect the two halves of the muscle toward the origin and insertion, clearing the fat, etc., from the inner surface of the muscle and the parts covered by it. Determine origin and insertion.

2. The acromiotrapezius (Fig. 68, _h_). Dissect in the same manner, being careful not to injure the broad thin tendon which connects the two muscles across the middle line.

3. The clavotrapezius (Fig. 68, _d_). Separate it carefully, from the cleidomastoid (p. 120). Transect and reflect, as before.

4. The occipitoscapularis (Fig. 73, _a_, p. 149). Note the strong fascia which separates it from the deeper muscles of the neck. Be careful not to injure adjacent muscles in tracing this toward origin and insertion. Transect.

5. The rhomboideus. Transect.

Recognize the levator scapulæ ventralis (Fig. 68, _f_), the sternomastoid (Fig. 68, _c_; Fig. 65, _g_), and the cleidomastoid (Fig. 65, _h_). Then dissect--

6. The levator scapulæ ventralis (Fig. 68, _f_). Its origin (Fig. 72, _c_, _c′_) cannot be seen at this stage and should be left until the cervical muscles are dissected. Be careful in transecting this muscle to separate it well from the cleidomastoid. Transect.

7. The cleidomastoid (Fig. 65, _h_). Its origin cannot be fully seen at this stage. Transect.

Make a midventral incision of the skin from the cranial end of the manubrium to a point opposite the crest of the ilium. From the caudal end of this incision make an incision to the root of the tail. From the cranial end of the incision in the ventral middle line make a cut around the base of the fore limb on its caudal side, thus connecting the ventral incision with the incision which passes between the manubrium and the thirteenth thoracic vertebra.

Make another incision from the convexity of the knee at the joint along the fold of the skin which connects the hind limb and body, to the incision which leads to the root of the tail.

Reflect the flaps thus formed so as to expose the body and flank, removing the skin-muscle with the skin.

8. The latissimus dorsi (p. 121, and Fig. 68, _m_). Dissect it up and transect it. Work carefully toward its insertion and note the origin from its outer surface in the axilla of a part of the cutaneus maximus, and at about the same place of a thin muscle, the epitrochlearis (p. 164, and Fig. 65, _r_), _without_ determining the insertion of the latissimus.

9. Dissect the pectoralis group of muscles (Fig. 65, and p. 144), i.e., the pectoantibrachialis (Fig. 65, _m_), the pectoralis major (_l_), pectoralis minor (_o_), and xiphihumeralis (_p_).

Determine the border of each muscle before lifting it, then work it up at its middle, transect it, and work toward its ends, determining origin and insertion.

Refer constantly to the skeleton.

10. Then recognize the teres major (p. 163, and Fig. 75, _d_; Fig. 77, _c_) and the common insertion of the teres major and latissimus (Fig. 79, _d′_); find the bicipital arch (Fig. 65, _t′_) and determine its composition (p. 166).

11 and 12. The serratus anterior and levator scapulæ (Fig. 73, _h_ and _i_, and p. 122). In order to expose the origin of these muscles, the external oblique muscle (Fig. 68, _p_) must be recognized, and that part of it which has its origin from the fourth to the ninth rib should be transected about an inch and a half from its origin and reflected.

The thoracic portion of the rectus abdominis (Fig. 73, _k_) and of the scalenus (Fig. 73, _f_-_f‴_) should also be recognized and then raised at their outer borders and displaced toward the median line. _No part_ of any of these muscles should be removed or cut except as directed.

The serratus anterior and levator scapulæ should be transected and reflected to get at their origin and insertion.

B. _Muscles of the Arm_ (p. 156).--The arm is thus removed from the body and the dissection may be continued on the separated arm.

13. The clavobrachial (Fig. 65, _k_, and p. 157). Its origin is best seen later. Dissect it up, but do not transect it.

Search now with great care for the coracobrachialis. Consult the figures (Fig. 79, _c_) and descriptions (p. 164), and be especially careful not to injure the long head of the muscle and its tendon.

14. Dissect the coracobrachialis (Fig. 77, _f_). Cut and reflect it.

15. The subscapularis (Fig. 77, _a_, and p. 161). Near its glenoid end, its glenoid and coracoid borders are separated by triangular intervals from the adjacent muscles. Transect the muscle by a line connecting the apices of these triangles. Carry an incision from the middle of this one to the middle of the vertebral border of the scapula, and reflect the muscle on both sides of this incision,--thus determining its area of origin. Reflect the humeral end without injuring the capsule of the joint.

16. Dissect the supraspinatus (Fig. 75, _a_, and p. 159). Cut the strong fascia free from the border of the scapula and its spine. Then transect the muscle and reflect it, being careful not to injure the capsule of the joint.

17. The spinodeltoideus (Fig. 75, _e_, and p. 156). Find its two borders, beginning with the caudal one. In freeing the very short cranial border do not injure the acromiodeltoideus (Fig. 75, _f_). Transect and reflect the spinodeltoid.

18. The acromiodeltoideus (p. 157, and Fig. 75, _f_). Transect and reflect.

19. The infraspinatus (p. 160, and Fig. 75, _c_). Locate the borders in the region of the great scapular notch. It is difficult to separate the glenoid border from the adjacent teres minor (Fig. 80, _c_). The separation should be begun at the humerus. Transect the muscle at the great scapular notch and reflect. Be careful not to injure the teres minor (Fig. 80, _c_).

20. The teres major (p. 163, and Fig. 75, _d_; Fig. 77, _c_) should be cut near its junction with the latissimus dorsi (Fig. 77, _e_).

21. The teres minor (Fig. 80, _c_, and p. 161) need not be cut.

22. The epitrochlearis (p. 164, and Fig. 65, _r_).

23. The triceps (p. 166). (_a_) The long head of the triceps (Fig. 77, _i_; Fig. 75, _g_). Find first its medial border and separate it from the medial head. Note the union of its lateral surface with the dorsal border of the lateral head by strong fascia, and then cut the fascia.

(_b_) The lateral head (Fig. 75, _h_).

(_c_) The medial head (Fig. 79, _g_, _h_, and _j_).

24. The anconeus (p. 170, and Fig. 80, _l_).

25. The brachioradialis (p. 173, and Fig. 75, _k_). Reflect it carefully to its origin and insertion.

26. The biceps (Fig. 77, _g_, and p. 165). The capsule of the shoulder-joint may be opened in order to expose its origin. Its insertion cannot be seen at this stage.

27. The brachialis (Figs. 75 and 79, _i_, and p. 166). Work under it near its union with the clavobrachial; cut it at that point and reflect it.

28. Extensor carpi radialis longus (p. 173, and Fig. 75, _l_). Note the oblique tendon on the radial side of the wrist near the insertion of the brachioradialis. A second tendon passes beneath its distal border. This tendon may be separated into a deep and superficial portion. The latter may be traced proximad to its muscle, the extensor carpi radialis longus.

29. Extensor carpi radialis brevis (p. 174). Its tendon is the deeper of the two tendons seen when isolating the tendon of the extensor longus.

30. Extensor communis digitorum (p. 174, and Fig. 75, _m_).

31. Extensor lateralis digitorum (p. 175, and Fig. 75, _n_).

32. Extensor carpi ulnaris (p. 176, and Fig. 75, _o_).

33. Extensor indicis (p. 176, and Fig. 85, _c_).

34. Pronator teres (p. 179, and Fig. 77, _q_).

35. Flexor carpi radialis (p. 179, and Fig. 77, _r_). The tendon of the flexor carpi radialis should not be traced to its insertion until the deep muscles of the palm of the hand have been dissected.

36. Abductor brevis pollicis (p. 184, and Fig. 77, _w_).

37. Flexor carpi ulnaris (p. 180, and Fig. 77, _t_).

38. Palmaris longus (p. 179, and Fig. 77, _s_). In dissecting this muscle be careful not to injure the part of the flexor sublimis (Fig. 77, _x_) that rises from its surface (see flexor sublimis, p. 181). Cut the palmaris proximad of the origin of the flexor sublimis and reflect it.

39. Flexor sublimis digitorum (p. 181 and Fig. 77, _x_). Trace one or two of the tendons through the sheaths on the ventral surfaces of the first phalanges. Cut and reflect the radial portion.

40. Flexor profundus digitorum (p. 181, and Fig. 77, _u_). After recognizing the parts cut through the tendons of the first and fifth parts and reflect them to determine their origin. Then cut through the common tendon so as to reflect the other three parts together. Trace one or two of the tendons to the distal end of the digit.

41. The supinator (p. 177, and Fig. 85, _b_).

42. The extensor brevis pollicis (p. 178, and Fig. 85, _a_).

43. Pronator quadratus (p. 183, and Fig. 87, _a_).

The insertion of the brachialis and clavobrachial (Fig. 87, _c_) and of the biceps (Fig. 87, _b_) should now be examined.

There remain to be dissected the small muscles of the palm of the hand. If these have been injured on the side dissected, the hand of the other side may be used.

44. The lumbricals (p. 184, and Fig. 88, _f_).

45. The flexor brevis pollicis (p. 184, and Fig. 89, _a_).

46. The adductor pollicis (p. 185, and Fig. 89, _b_).

47. The abductor digiti quinti (p. 185, and Fig. 89, _i_).

48. The flexor brevis digiti quinti (p. 186, and Fig. 89, _h_). Cut and reflect it.

49. The opponens digiti quinti (p. 186, and Fig. 89, _g_). Cut and reflect it.

50. The interossei (p. 185, and Fig. 89).

IV. MUSCLES OF THE NECK AND THE DEEP MUSCLES OF THE HEAD.

If the superficial muscles of the head have been dissected according to the directions above given (p. 434), the skin of the head and neck, and the external ear, will have been removed, and the specimen is ready for further study. The parotid and submaxillary glands (Fig. 65, 1 and 2) should be removed if this has not been done; also the lymphatic glands (Fig. 65, 3).

If the superficial muscles of the head have not been dissected and are not to be, remove the skin from the side of the neck, head, and face to the median dorsal line, removing the thin superficial muscles with the skin. Remove also the parotid, submaxillary, and lymphatic glands (Fig. 65, 1, 2, and 3), and cut through the ear-muscles and the cartilaginous auditory meatus (under direction) and remove the external ear. Clean fat, connective tissue, etc., from the surface of the muscles of the thorax, neck, and head; then dissect as follows:

1. The sternomastoid (p. 139, and Fig. 65, _g_). Transect and reflect it.

2. The cleidomastoid (p. 120, and Fig. 65, _h_). This has already been transected; examine now its origin.

Remove the large lymphatic gland beneath the sternomastoid and close to the tympanic bulla, and clean the surface of the muscles in this region.

3. The levator scapulæ ventralis (p. 120, and Fig. 72, _c_, _c′_, _c″_). This has already been cut; study now its origin.

4. The sternohyoid (p. 140, and Fig. 65, _e_). In raising it begin at the cranial end and take care not to injure the subjacent sternothyroid (Fig. 65, _g′_). Transect.

5. The sternothyroid (p. 141, and Fig. 65, _g′_). Transect.

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.