MUSCLES OF THE TBUNK. 255 



B. The posterior or deep portion (Fig. 159, 9) is a second muscular band, 

 shorter and stronger than the preceding. It is attached, above, to the transverse 

 processes of the first four cervical vertebrae by as many fleshy bands (Fig. 159, 8), 

 which cover the superficial portion. The upper digitation, given off to the atlas, 

 is united to the tendon common to the trachelo-mastoideus and splenius (Figs. 

 162, 9 ; 163, 9, 10, 11). The inferior extremity of this portion of the muscle 

 widens on the scapulo-humeral angle, which it envelops in becoming closely united 

 to the anterior portion, terminating with it on the humerus. An aponeurosis, 

 which is confounded with that of the trapezius, and sends off a septum into the 

 interstice between the two portions of the long abductor of the arm, concurs to 

 fix this extremity by spreading over the muscles of the arm. 



Relations. — It is covered, near its mastoid insertion, by the parotid gland and 

 the cervico-auricularis muscles ; for the remainder of its extent, by the aponeu- 

 rosis of the cervical panniculus, from which it is separated by a thin fascia con- 

 tinuous with that which extends over the trapezius. It covers the splenius, 

 trachelo-mastoideus, oblique muscles of the head, subscapulo-hyoideus (to which 

 it adheres intimately), the digastricus, long flexor of the head, the angularis, 

 scalenus, small pectoral, supra- and infra-spinatus muscles, the long abductor of 

 the arm, and the coraco-radialis. 



Action. — When the superior is the fixed point, it carries the entire anterior 

 limb forward. This muscle, therefore, plays a very important part in locomotion, 

 as it is called into action when the animal raises the fore limb in getting over the 

 ground. If the fixed point of the muscle is the limb, it inclines the head and 

 neck to one side. 



3. Steeno-maxillaeis (Figs. 159, 10 ; 174, 4). 

 Synonym. — The sterno-mastoideus of IVfon. 



Form — Structure — Situation — Direction — Attachments. — ^A long narrow muscle, 

 almost entirely fleshy, and terminated at its upper extremity by a flattened tendon ; 

 situated in front of the neck, beneath the panniculus, and parallel to the anterior 

 border of the supei'ficial portion of the mastoido-humeralis, from which it is 

 separated by a space that lodges the jugular vein ; attached, inferiorly, to the 

 cariniform cartilage of the &ternnm—fix£d insertion; and superiorly — movable 

 insertion — to the curved portion of the posterior border of the maxiUaiy bone by 

 its terminal tendon. 



Relations. — The muscle is covered by the panniculus, and the parotid gland. 

 It covers the trachea, the subscapulo-hyoideus, sterno-thyro-hyoideus, and the 

 maxillary gland. Its external border, parallel to the anterior border of the 

 mastoido-humeralis, forms with it a longitudinal depression termed the jugular 

 furroiv, because it lodges the vein of that name. Its inner border is intimately 

 united, in its lower third, to that of the opposite muscle. 



Action. — It directly flexes the head, when acting in concert with its congener ; 

 but alone it turns it to one side. Lafosse and Rigot have wrongly considered 

 this muscle as a depressor of the lower jaw, Bourgelat has correctly stated that 

 it cannot move this jaw independently. (Percivall says that the pair will assist 

 in opening the mouth ; and Leyh asserts that when the mouth is closed, each 

 muscle will act as a flexor to the head.) 



4. Steeno-thyeo-htoideus (Fig. 174, 6, 7). 

 Form — Structure — Situation — Attachments. — Small, ribbon-shaped, long, and 



