Dissected so as to show some of the muscles of the head, neck, shoulder, and fore-leg 1. The letters and the description correspond with those on the figure annexed.
With Figure 1.
The skin has been removed from the front of the lower jaw backwards, the sheet of cutaneous muscle, x, covering the region of the neck and known in anthropotomy as the panniculus carnosus or platysma myoides, has been entirely removed on the right side, as also from the region of the thorax on both sides; the incomplete clavicle with the muscles in connection with it has been separated from its ligamentous union with the sternum and displaced to the right so as to show the subjacent nerves, phrenic and brachial, on the same side; below the level of the clavicle, portions of the pectoral, c, d, and the sterno-claviadar muscles, g, have been dissected and turned back. On the left side, the anterior part of the panniculus carnosus has been left with its two fixed insertions, x and xr, into the lower jaw, and the other, x"', into the sternum, intact; the clavicle is left in situ, but the muscles passing down to it from the head have been cut away behind the line of the cutaneous muscle to show the sterno-scapular muscles, h and i, in connection with the clavicle, at j; and the serratus magnus, 0. The deep cervical fascia (B) is seen to the left of the middle line of the upper half of the neck and of the intermandibular space, at a lower level than the panniculus carnosus.
It has been removed anteriorly to show the insertion of the digastric muscle. On a level with the hyoid the deep cervical fascia is raised into a convexity (a) by the submaxillary gland underlying it, and it furnishes, externally and posteriorly to this area, a capsule to the parotid. This gland, however, being less convex than the submaxillary, does not cause the sheet of fascia to bulge upwards. On the opposite side this fascia has been removed in the intermandibular space; and the submaxillary gland being raised from its bed is seen to send a duct in towards the mouth in an interspace between the internal pterygoid and digastric muscles. This latter muscle is in the Rabbit, as in many other mammals, monogastric, its posterior belly being represented by a tendon, which however pierces the stylo-hyoid just as in man. Its muscular portion is inserted into the lower jaw on either side of the symphysis, and from the same portion of the jaw a depressor, w, of the lip passes forward. On the outer side of each of these depressor muscles the panniculus eamosus, x, x, x", takes a fixed insertion by a band of muscular fibres, which on the right side are cut short, and on the left are seen to be continuous with the rest of the muscle.
In the interval between this strip of muscle and another which passes from the platysma to distribute itself in the region of the mouth, the buccinator muscle, y, comes into view. The lobes of a somewhat variable buccal gland have been removed to show these three muscles in this region.
1 It is for various reasons advisable that the student should proceed to the preparations illustrating the splanchnology of the Rabbit before addressing himself to this somewhat complex dissection. And it will be found advantageous to immerse the upper half of the body of the animal, the heart and lungs having been removed, in spirit io° over proof (sp. gr.° 910) for three or four days before following out the detailed anatomy of the muscles here described and figured. For making special dissections of the nerves it will be found useful to acidulate the spirit with dilute nitric acid in the proportion of one part in forty. This treatment facilitates the mechanical process of dissection in several ways, and makes it less easy to overlook the more delicate structures concerned.
The tendon of the stylo-hyoid forms an oblique angle with its muscular belly, s, being connected with the greater cornu of the hyoid, along which it passes to be attached to the body of the bone, t. To the muscular part of the stylo-hyoid two nerves, from the portio dura of the seventh pair with which the glosso-pharyngeal portion of the eighth pair of cranial nerves is connected, may be seen in dissection under a lens, though not in this figure, to distribute themselves. A semilunar space has been formed in the right axilla, between δ and γ by separating the latis-simus dorsi, γ, as it narrows up to its insertion on the inner side of the humerus, from the similarly narrowing panniculus eamosus, 8, of the regions of the flanks and back, the 'dermo-humerien' of Cuvier (Anat. Comp. iii. p. 597), the 'costo-alaris' of Humphry (Observations in Myology, p. I3I), which passes in front of it to be inserted into the humerus together with the tendon of the pectoralis major. The insertion of the homologous muscle in Birds is shown in the figure of the Dissection of the Pigeon in the shape of a tendinous slip attached to the tendon of the great depressor pectoral muscle, x.
From the tendon of the latissimus dorsi of the left side a slip of muscle, the 'latissimo-condyloideus' of Bischoff 1, the 'dorso-epitrochlien' of Duvernoy (Archiv. du Museum, viii. p. 80), is seen to take origin and pass down at right angles to that tendon to an insertion on the inner side of the olecranic process of the ulna. On either side and behind the latissimo-condyloideus are to be seen the three heads of the triceps, with which muscle the latissimo-condyloideus is frequently fused. Externally and anteriorly is seen the biceps, 6, here, like the similarly misnamed digastric, but a monogastric muscle. From its anterior surface, one band of fascia passes off to connect itself with the fascia enveloping the muscles of the fore-arm, another leaves the tendon of the muscle at a lower level and connects itself with the radius and the tendon of the pronator radii teres, thereby setting up a secondary connection with the radius with which it is principally connected in man, whilst its principal insertion is made into a well-marked depression just above the inner and inferior edge of the olecranic process of the ulna by a broad and flat tendon.