314 THE MUSCLES OF THE TRUNK. 



Relations. The splenius is covered below and internally by the trapezius, the rhomboids 

 and the serratus posticus superior ; and at its insertions by the sterno-mastoid and levator 

 anguli scapulas : between these the splenius capitis is exposed in the posterior triangular 

 space. The muscle conceals, in part, the spinalis dorsi, the complexus and the trachelo- 

 mastoid. The splenius represents the prolongation to the head and upper cervical vertebra 

 of the outer division of the erector spinse. 



Varieties. The origin of the splenius is frequently moved upwards to the extent of one 

 or two vertebrae. Absence of the splenius colli has been observed in a negro (Testut). The 

 rJionibo-atloideus or splenius colli accessor ins is a muscular slip occasionally present, arising 

 from one or two lower cervical or upper dorsal spines, superficial to the serratus posticus 

 superior, and inserted into the transverse process of the atlas. The name gjflenitfx ca^ltix 

 accessories may be given to a similar slip ending on the occipital bone or the mastoid process. 



ERECTOR SPINSE. This is a large composite muscle, extending throughout the 

 whole length of the back from the pelvis to the head, and divided for purposes of 

 description into seven parts, to which distinct names are applied. Commencing 

 below as a common mass, it is continued upwards in three columns, of which the 

 innermost, spinalis dorsi, is comparatively slender and short, while the other two are 

 much thicker, and are again subdivided each into three portions, viz., in the outer 

 column, ilio-costalis, accessorius, and cervicalis ascendens, and in the middle column, 

 longissimus dorsi, transversalis cervicis, and trachelo-masioid. 



The origin of the erector spinse takes place mainly by means of a strong flattened 

 tendon, which is attached to the lowest two or three dorsal and all the lumbar and 

 sacral spines, to the posterior fifth of the iliac crest, and to the lower and back part 

 of the sacrum, as well as to the ligaments uniting that bone to the coccyx. This 

 tendon becomes blended below with the overlying layer of the lumbar fascia : its 

 deep surface gives origin also to some fibres of the multifidus spinae ; and between 

 the iliac and sacral attachments a part of the gluteus maximus arises from its border. 

 The fasciculi of which it is composed pass nearly vertically upwards, the outer ones, 

 above the iliac crest, being very short, while the inner ones ascend by the side of the 

 spines to the middle of the dorsal region. The fleshy fibres of the muscle are derived 

 mostly from the oblique upper border and the deep surface of the tendon, but others 

 spring directly from the rough posterior part of the inner surface of the ilium, 

 beneath and outside the attachment of the tendon. The lower part of the muscle 

 forms a large mass which projects backwards beyond the spines, and laterally beyond 

 the transverse processes of the lumbar vertebrae, and which becomes divided below 

 the level of the last rib into the middle and outer columns. The inner column only 

 separates itself from the middle column in the upper dorsal region. 



a. The ilio-costalis or sacro-lumbalis, the first portion of the outer column, 

 is continued from the outer and superficial portion of the common mass. It ends 

 in a series of tendons which incline slightly outwards, and are inserted one into each 

 of the lower six or seven ribs at their angles ; a slender fasciculus is usually prolonged 

 also into the accessorius, and contributes to the formation of the lower two or three 

 tendons of insertion of that muscle. 



1). The musculus accessorius ad ilio-costalem (ad sacro-lumbalem) prolongs 

 upwards the preceding muscle. It arises by flat tendons from the upper margins of 

 the lower six ribs, internal to the tendons of the ilio-costalis, and ends above by 

 continuing the series of those tendons to the angles of the upper ribs, and to the 

 transverse process of the seventh cervical vertebra. 



c. The cervicalis asceudens consists of slips in serial continuation with the 

 foregoing, taking origin from four or five ribs above the accessorius, and inserted 

 into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth 

 cervical vertebras. Its insertions are intimately connected with those of the trans- 

 versalis cervicis. 



d. The longissimus dorsi is both larger and longer than the ilio-costalis, its 



