wards. Some of the lower muscles pass in part over the first rib below their origin, to be attached to the next one; these have been called the levatores longiores costarum.

The INTERSPINALES extend between the spinous processes. Between the dorsal vertebræ they can hardly be said to exist, and are very small in the lumbar region. In the neck, they are found in pairs, corresponding to the bifid condition of the spinous processes. Some of them pass over one or more vertebræ, and are called supra-spinous. There is none between the first two vertebræ.

The INTERTRANSVERSALES, Fig. 98 (18), are a series of short muscles, extending between the transverse processes. In the neck, they consist of two fasciculi, an anterior and posterior. In the dorsal region they are generally wanting, excepting between the last two vertebræ. In the lumbar region they are smaller than in the neck. They support the spine, and

bend it to one side.

Between the occiput and the upper cervical vertebræ are several small muscles, which are worthy of more attention than some of the preceding.

They are deep-seated, and, to dissect them, the position of the head must be changed, so as to render them tense.

This group of muscles is separated from the complexus by an aponeurosis and dense areolar tissue. They consist of two obliqui and two recti, on each side; between these will be found a triangular space, occupied by fat and areolar tissue, and containing, also, the posterior division of the suboccipital nerve, which is distributed to those muscles, a plexus of veins, and the vertebral artery.

The RECTUS CAPITIS POSTICUS MAJOR, Fig. 98 (13), arises from the spinous process of the second vertebra, passes upwards, and is inserted into the inferior transverse ridge of the occipital bone. It is of a triangular shape, being broad above and narrow below. It is covered by the complexus, and the superior oblique partly overlaps its insertion.

The RECTUS CAPITIS POSTICUS MINOR, Fig. 98 (12), is a very small muscle, situated beneath the major. It arises from the spinous process of the first cervical vertebra, and is inserted into the occipital bone, between the inferior transverse ridge and the occipital foramen. The small recti muscles are situated nearer to the median line than the large. The recti

muscles draw the head backwards, or to one side. The large recti may assist in rotating it, or moving it on the axis.

The OBLIQUUS CAPITIS INFERIOR, Fig. 98 (15), arises from the spinous process of the second vertebra, goes upwards and outwards, and is inserted into the transverse process of the atlas. It moves the atlas round the odontoid process, and thus assists in rotating the head.

The OBLIQUUS CAPITIS SUPERIOR, Fig. 98 (14), arises from the transverse process of the atlas, and passes upwards and inwards, and is inserted into the occipital bone just above the insertion of the rectus major, which is partly covered by it. The upper part of this muscle is broad and aponeurotic. It bends the head backwards and to one side.

After the muscles on the back of the neck have been dissected, the vertebral artery may be examined in its course through the transverse processes, and as it enters the foramen occipitale. It is accompanied by the vertebral vein.

The great number of muscles on the back, with their numerous attachments, renders this part of the body somewhat difficult of dissection and study. Few students have the time and patience to learn all these muscles and their attachments, and, when it is done, the knowledge thus acquired cannot long be retained. Yet the dissection of the back should not be neglected; it should receive a portion of the time and attention of every student.

In

Instead of attempting to recollect the exact origin and insertion of each muscle, or any mere arbitrary division based upon their arrangement in layers or strata, he should rather endeavor to fix them in his mind according to their individual or combined action. As, for example, he should arrange and classify in his own mind all those muscles which act directly or indirectly on the shoulder, and through the shoulder on the arm or on the walls of the thorax, as in respiration. this way he will learn what muscles are at fault in displacements of the scapula, or in curvatures of the spine depending on a loss of antagonism in the muscles of the two sides, or of tone in those of both sides. All the muscles concerned in supporting or moving the head should be grouped together as acting in unison, and also those which act on the vertebral column, but not as acting on separate vertebræ so much as on its different sections. When the muscles of the back are studied

in this way, classified according to their functions, they become an interesting portion of the animal economy. A knowledge of the exact relations of the muscles of the back to each other is not so important as in many other parts of the body, where there are large vessels and nerves, or other important organs, in relation with them.

SECT. III.-DISSECTION OF THE SHOUlder.

In detaching the upper extremity from the trunk, it is desirable to disarticulate the clavicle from the sternum; but it frequently happens that the dissection of the head and neck is not sufficiently advanced to allow of this, at least on both sides, without injuring those parts. In this case, the clavicle should be left attached to the trunk while the scapula is removed with the arm, by separating it at the acromio-clavicular articulation. Even the removal of the scapula will interfere more or less with the lower part of the side of the neck, but not materially, if the back of the neck has been fully dissected. The vessels and nerves in the axilla should be tied together, so that they can be made tense by fastening them to something with hooks or twine.

In dissecting the arm, no specific rules can be laid down in regard to the position. The student must select such position as will put the muscle or muscles which he is dissecting on the stretch, or allow him to trace with the greatest facility the vessels and nerves as he proceeds in his dissection.

The anterior part of the DELTOID was, Fig. 90 (8), exposed with the clavicular portion of the pectoralis major; the remainder of it, Fig. 100 (13), may now be dissected by continuing the dissection from before backwards. The skin may be raised first, so as to examine the deltoid fascia and to trace the supra-acromial branches, Fig. 103 (1), from the cervical plexus of nerves, and cutaneous branches (2) from the circumflex nerve which is reflected over the posterior margin of the muscle; or the student may remove the skin and fascia from the muscle at the same time. This muscle is composed of very large fasciculi, each one of which seems to be a small muscle of itself.

It arises, tendinous and fleshy, from the outer third of the clavicle, from the acromion process and spine of the scapula;

Fig. 99.

its fibres converge to form a short, thick tendon, which is inserted into the deltoid ridge of the humerus. This muscle may be divided into anterior, middle, and posterior portions. It will be seen, from the origin and insertion of the deltoid, that it is of a triangular form, and covers all the outer part of the shoulder-joint. Its action is to raise the arm, and to keep the head of the humerus applied to the glenoid cavity. If the posterior fibres act alone, they will draw the arm upwards and backwards, while the anterior fibres, acting alone, will draw it upwards and forwards. Its origin corresponds to the insertion of the trapezius.

A VIEW OF THE DELTOID MUSCLE.-1. Clavicle. 2, 3,

4.

Origin of the deltoid from the clavicle, acromion, and spine of the scapula. 5. Body of the scapula. 6. Middle of the deltoid, showing the fasciculated character of its fibres. the os humeri.

This muscle should be raised by detaching it from its origin and reflecting it downwards. In dissecting it up from the humerus, the anterior and posterior circumflex arteries and the circumflex nerve will be observed entering its under surface. It will be seen that a blow over the deltoid might, by injuring the circumflex nerve, paralyze this muscle. There is also to be noticed a large bursa between it and the upper and outer part of the humerus. Its relations to the shoulderjoint and the parts around it are deserving of special attention. It will be observed that its under surface is more tendinous than the outer, and that many of the muscular fasciculi terminate in a tendinous structure some distance from the point of insertion.

The deltoid muscle is to be preserved, in order to replace it after the parts which are covered by it have been dissected. It is only in this way that its relations can be properly understood.

The SUPRA-SPINATUS, Fig. 100 (2), occupies the supra-spinata fossa. It is covered by the trapezius, and by a thick, dense aponeurosis, named the supra-spinous fascia. This fascia is attached to the margins of the fossa, and sends a process for

THE UPPER EXTREMITY.

wards, to be lost in the tendon of the supra-spinatus muscle. Removing this fascia, the muscle will be exposed. It arises from the surface of the whole fossa, except the anterior part, and also from the under surface of the fascia, posteriorly. It passes beneath the acromion process, and ends in a tendon which is inserted into the upper part of the great tuberosity of the humerus.

Its tendon is blended with the capsular ligament of the joint, over which it passes. There is a great deal of loose areolar tissue situated around this muscle, where it passes under the acromion process and the coraco-acromial ligament. It assists the deltoid in raising the arm, and, when it is raised, prevents the head of the humerus from being displaced into

Fig. 100.

4.

A POSTERIOR VIEW OF THE MUSCLES OF THE SHOULDER, WITH THE DELTOID.1. Acromion scapula. 2. Supra-spinatus muscle. Posterior portion of the origin of the deltoid. 5. Infra-spinatus muscle. 6. Teres major. 7. Teres minor. 8. Long head of the triceps extensor. 9. Its second head. 3. Spine of the scapula. 10. The shaft of the os humeri. deltoid. 13. Its middle portion forming the round part of the shoulder. 11. Brachialis anticus. 12. Insertion of the

the axilla, by keeping it firmly applied to the glenoid cavity; it also draws the capsular ligament from beneath the acromion process, when the head of the humerus is pressed against it. In raising the supra-spinatus, the supra-scapular artery and nerve are to be traced. spinata fossa by passing under the acromion process, where They are continued into the infrathey will be met with when the infra-spinatus muscle is dissected. The nerve usually passes through the coracoid notch, to enter the supra-spinata fossa, while the artery generally passes over the ligament which subtends this notch and con