MUSCLES OF THE TRUNK 267 



Action. — It either directly flexes the head or carries it to one side, according 

 as it acts alone or with its fellow of the opposite side. 



7. Small Anterior Straight Muscle of the Head (Rectus Capitis 

 Anticus Minor). 



Synonyms. — Flexor capitis brevis — Bourgelat. Atloido-suboccipitalis— Girard. (Rectiis 

 capitis anticus minor — Fercivall. Atloido-oocipitalia inferior — Leyh.) 



A small, entirely fleshy, prismatic fasciculus, lying to the external side of the 

 preceding muscle ; attached, posteriorly, to the inferior face of the body of the 

 atlas ; in front, to the body of the sphenoid bone and the basilar process, beside 

 the great anterior straight muscle. It is covered by the guttural pouch, and 

 covers the occipito-atloid articulation. It concurs in flexing the head. 



8. Small Lateral Straight Muscle (Rectus Capitis Lateralis). 



Synonyms. — Flexor capitis parvus — Bourgelat. Atloido-styloideus — Girard. (Obliqum 

 capitis anticus — Percivall. The rectus capitis lateralis of Man.) 



Smaller than the preceding, and prismatic and entirely fleshy, like it, this 

 muscle lies on the side of the occipito-atloid articulation ; it is attached to the 

 atlas, outside the small anterior straight mu&cle— fixed insertion ; and to the inner 

 face of the styloid process of the occipital bone — movable insertion. It is the 

 congener of the two anterior straight muscles of the head. 



9. Scalenus (Figs. 161, 162, 163). 



Synonyms. — Costo-tracheleus — Girard. (Scalenus anticus and posticus of Man.) 



Sitimtion — Direction — Composition. — Deeply situated at the inferior part of 

 the neck, in an oblique direction downwards and backwards, this muscle com- 

 prises two portions of unequal dimensions, placed one above another. 



Form — Structure — Attachments. — A The superior portion {scalenus posticus 

 of Man), the smallest, is composed of three or four fleshy fasciculi, attached by 

 their extremities to the transverse processes of the last thi-ee or four cervical 

 vertebras. The last terminates at the superior extremity of the first rib. 



B. The inferior {scalenus anticus of Man), the most considerable, is flattened 

 on both sides, thick and wide posteriorly, thin and naiTOw anteriorly, and is 

 composed almost entirely of fleshy fibres which are longest as they are inferior. 

 It is attached : 1. To the transverse processes of the last four cervical vertebrae 

 by short fasciculi scarcely distinct from one another, the first of which is crossed 

 by the last digitation of the great anterior straight muscle. 2. To the anterior 

 border and external face of the first rib, where all its fibres end. 



Relations. — The scalenus responds : by its external face, to the subscapulo- 

 hyoideus, mastoido-humeralis, and the deep pectoral ; by its internal face, 

 to the longus colli, trachea, common carotid artery and its accompanying nerves, 

 and — on the left side only — to the oesophagus ; by its inferior border, to the 

 jugular vein. The two portions of the scalenus are separated from each other, in 

 front of the first rib, by an interspace traversed by the nei-ves of the brachial plexus. 



Action. — When the first rib is the fixed point, this muscle either directly 

 flexes the neck or inclines it to one side. When the neck is the fixed point, it 

 draws forward the first rib and fixes it in this position dm'ing the dilatation of 

 the chest, in order to aid the inspiratory action of the external intercostal muscles. 



