MYOLOGY 



into the oblique line on the lamina of the thyroid cartilage. This muscle is in 

 close contact with its fellow at the lower part of the neck, but diverges somewhat 

 as it ascends; it is occasionally traversed by a transverse or oblique tendinous 

 inscription. 



Variations. Doubling; absence; accessory slips to Thyreohyoideus, Inferior constrictor, or 

 carotid sheath. 



The Thyreohyoideus (Thyrohyoid muscle) is a small, quadrilateral muscle 

 appearing like an upward continuation of the Sternothyreoideus. It arises from 

 the oblique line on the lamina of the thyroid cartilage, and is inserted into the 

 lower border of the greater cornu of the hyoid bone. 



The Omohyoideus (Omohyoid muscle) consists of two fleshy bellies united by 

 a central tendon. It arises from the upper border of the scapula, and occasionally 

 from the superior transverse ligament which crosses the scapular notch, its extent 

 of attachment to the scapula varying from a few millimetres to 2.5 cm. From 

 this origin, the inferior belly forms a flat, narrow fasciculus, which inclines forward 

 and slightly upward across the lower part of the neck, being bound down to the 

 clavicle by a fibrous expansion; it then passes behind the Sternocleidomastoideus, 

 becomes tendinous and changes its direction, forming an obtuse angle. It ends 

 in the superior belly, which passes almost vertically upward, close to the lateral 

 border of the Sternohyoideus, to be inserted into the lower border of the body 

 of the hyoid bone, lateral to the insertion of the Sternohyoideus. The central 

 tendon of this muscle varies much in length and form, and is held in position by 

 a process of the deep cervical fascia, which sheaths it, and is prolonged down to 

 be attached to the clavicle and first rib; it is by this means that the angular form 

 of the muscle is maintained. 



Variations. Doubling; absence; origin from clavicle; absence or doubling of either belly. 



The inferior belly of the Omohyoideus divides the posterior triangle of the neck into an upper 

 or occipital triangle and a lower or subclavian triangle, while its superior belly divides the anterior 

 triangle into an upper or carotid triangle and a lower or muscular triangle. 



Nerves. The Infrahyoid muscles are supplied by branches from the first three cervical nerves. 

 From the first two nerves the branch joins the hypoglossal trunk, runs with it some distance, 

 and sends off a branch to the Thyreohyoideus; it then leaves the hypoglossal to form the descendens 

 hypoglossi and unites with the communicantes cervicalis from the second and third cervical nerves 

 to form the ansa hypoglossi from which nerves pass to the other Infrahyoid muscles. 



Actions. These muscles depress the larynx and hyoid bone, after they have been drawn up 

 with the pharynx in the act of deglutition. The Omohyoidei not only depress the hyoid bone, 

 but carry it backward and to one or the other side. They are concerned especially in prolonged 

 inspiratory efforts; for by rendering the lower part of the cervical fascia tense they lessen the 

 inward suction of the soft parts, which would otherwise compress the great vessels and the 

 apices of the lungs. The Thyreohyoideus may act as an elevator of the thyroid cartilage, when 

 the hyoid bone ascends, drawing the thyroid cartilage up behind the hyoid bone. The Sterno- 

 thyreoideus acts as a depressor of the thyroid cartilage. 



IV. THE ANTERIOR VERTEBRAL MUSCLES (Fig. 387). 



The anterior vertebral muscles are: 



Longus colli. Rectus capitis anterior. 



Longus capitis. Rectus capitis lateralis. 



The Longus colli is situated on the anterior surface of the vertebral column, 

 between the atlas and the third thoracic vertebra. It is broad in the middle, 

 narrow and pointed at either end, and consists of three portions, a superior oblique, 

 an inferior oblique, and a vertical. The superior oblique portion arises from the 

 anterior tubercles of the transverse processes of the third, fourth, and fifth cervical 

 vertebrae; and, ascending obliquely with a medial inclination, is inserted by a narrow 



