passes from the upper edge of the transverse process of the atlas to the transverse or jugular process of the occiput: the latter, on a plane anterior to this, from the anterior root of the transverse process and side of the anterior arch, inclines upward and a little inward, to be inserted into the basilar process of the occipital bone behind the rectus capitis anticus major, between its outer edge and the foramen magnum. The rectus capitis lateralis separates the vertebral artery from the jugular vein.
These muscles in approximating their points of attachment can give lateral flexion to the neck and to the head.
The scaleni (Costo-trachelien: Chauss.) are situated at the lower lateral part of the neck, extending from the transverse processes to the first two ribs, and are of triangular form. They have been variously described by different anatomists, some considering their fleshy mass as a single muscle, others distinguishing in it two, three, and even five parts. I shall adopt the more usual modern division, which recognises two muscles, scalenus anticus and scalenus posticus.
Scalenus anticus arises from the third, fourth, and fifth cervical vertebræ, at the anterior tubercles and notched extremities of their transverse processes, by slips of tendon, to which muscular fibres directly succeed, and descends with an inclination outward and forward to be inserted by a flat strong tendon into a roughness about the middle of the anterior third of the first rib. This insertion is important as affording a guide to the position of the subclavian artery, which, in arching over the rib, lies behind this tendon and separates it from the insertion of the scalenus posticus. It is triangular in shape and fleshy in nearly its whole extent: externally it presents a free border, from behind which emerge the elements of the brachial plexus and the subclavian artery; internally its origin adjoins that of the rectus capitis anticus major, from which it is demarked by the arteria cervicalis ascendens, and toward its insertion is separated from the longus colli by a space in which the vertebral artery ascends; its anterior surface is crossed from above by the phrenic nerve, and transversely by branches of the thyroid axis; its deep surface is separated from the scalenus posticus by the emerging trunks of the nerves, and the space between them, broadening towards the first rib, includes there the brachial plexus and subclavian artery—the latter being below and in front of the former, and in immediate contact with the rib.
Scalenus posticus, larger than the preceding, behind which it is situated, arises by six tendons, to which muscular fibres directly succeed, from the posterior tubercles of the transverse processes of the six last cervical vertebræ. The first slip (often partly derived from the atlas) is joined, as it descends, by the others in succession, and a large triangular muscle results, which has its base at the transverse processes and its apex at the second rib. It is inserted, first, by an anterior broad slip into the outer edge of the first rib, from the tubercle behind a£ far forward as the arterial impression in front; secondly, by a smaller slip, which is prolonged from the posterior surface of the muscle to the upper edge of the second rib near its tuberosity. This muscle corresponds anteriorly to the scalenus anticus, from which it is separated by the brachial plexus and subclavian artery; posteriorly to the levator anguli scapulæ; by its inner edge to its points of origin; by its outer edge to the serratus magnus and transversalis colli artery, to branches of the cervical and brachial plexus of nerves, and to the sterno-mastoid muscle; lastly, by its inferior-internal edge to the longus colli, from which it is divided by the anterior branch of the first dorsal nerve, and by the (generally) common trunk of the deep cervical and first intercostal arteries.
The action of the scaleni, as of the muscles previously described, consists rather in maintaining steadiness and resisting lateralisation of the neck, than in effecting any considerable movement. They may, however, in a slight degree, bend the neck laterally. The vertebræ being fixed, their muscles by acting together may elevate the first two ribs and so assist in inspiration. The scalenus anticus can, from its advanced insertion, act more effectually thus. This action is illustrated in all deeper inspirations; for these differ from ordinary breathing therein, that the chest is expanded by the elevation of the ribs and sternum, in its antero-posterior and transverse diameters, in addition to the ordinary increase of capacity which it gains by the descent of the diaphragm; and in order to the effective action of the intercostals, the first rib must be rendered immoveable. The scaleni, in raising the anterior extremity of the first ribs, favour the advance of the sternum, and then rigidly fixing these bones enable the intercostal muscles to give to the ribs beneath that slight axial rotation by which the transverse diameter of the chest is increased.[1]
The intrinsic muscles of the larynx having already been described (see Larynx), and those of the pharynx being for future description (see Pharynx), our second class will comprise only the muscles of the os hyoides and tongue, viz. depressors of the os hoides, the sterno-hyoid, orno-hyoid, and sterno-thyroid, with its continuation the thyro-hyoid; its elevators, the digastric, stylo-hyoid, mylo-hyoid, genio-hyoid; muscles of the tongue, hyo-glossus, genio-hyo-glossus, and lingualis.
The sterno-hyoid and sterno-thyroid are two riband-like muscles, having respectively the attachments denoted by their names,—situated beside the median line, so as to be divided
- ↑ Within the last year I have observed in two subjects an importantly anomalous insertion of the scalenus anticus. Its main bulk of tendon passed on both sides to an insertion behind the artery, a very small slip only taking the usual course. The strong flat tendon, which is usually so trustworthy a guide to the artery, would in these cases have involved an operator in the misfortune of surrounding the nerves with his ligature; and the circumstance illustrates the necessity of trying the effect of temporary pressure on a supposed arterial trunk, before conclusively tightening the ligature around it.
