300 DORSAL MUSCLES OF THE TRUNK. 



columns, of which the inner, or that next the spine, is comparatively 

 slender ; the middle and outer columns are much thicker, and consist 

 each of three divisions wliich have received separate names. 



The erector spina? takes origin inferiorly as a common mass, the 

 outer part of which is nuiscular, while the inner and larger part is 

 tendinous. The muscular portion arises from the posterior lifth of the 

 crest of the iiium ; the tendinous portion arises from the back part of 

 the ilium, the lower and back part of the sacram, and the sacral and 

 lumbar spines ; it is inseparably united below with the lumbar aponeu- 

 rosis, and is prolonged upwards on the surface of the muscular part, 

 concealing the multifidus spina?. The division of the larger part into 

 the external and middle columns takes place below the level of the last 

 rib. 



The three parts of the outer columns are — 



a. The ilio-costalis (Theile) or sacro-lumbalis, the main muscle 

 of the outer column, is fleshy inferiorly, springing from that part of the 

 common origin which proceeds from the crest of the ilium ; it ends in 

 a series of tendons which incline slightly outwards, and are inserted 

 one into each of the six or seven lowest ribs at their angles. 



h. The niuscxilus accessorius ad ilio-costaleni (ad sacro-lnniba- 

 lem) is a continuation upwards of the precedmg 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 superiorly by continuing the 

 series of those tendons to the angles of the upper ribs. 



c. Tlie cervicalis ascendens consists of slips in serial continuation 

 with those of the musculus accessorius, taking origin from four or five 

 of the highest ribs, and inserted into the transverse processes of three 

 cervical vertebrse, usually the fourth, fifth, and sixth. Its insertions are 

 intimately connected with those of the transversalis cervicis. 



The middle column consists of 



d. The longissimus dorsi muscle. This muscle is both larger and 

 longer than the ilio-costalis, its original fibres passing as high as the 

 first dorsal vertebra. Internally it is closely connected on t!ie surface 

 with the spinalis dorsi, from the lower part of which it generally 

 receives one or more tendinous slips. When those slips and the 

 tendons of origin from the lumbar spines are cut through, the inner 

 surface of the muscle can be brought into view. The longissimus dorsi 

 presents two series of insertions. The inner row of insertions is a 

 series of rounded tendons attached to the inferior tubercles of all the 

 transverse processes of the dorsal, and the accessory processes of the 

 lumbar vertebra?. The outer insertions form a series of thin fleshy 

 processes which are attached in the dorsal region to the nine or ten 

 lowest ribs, between their tubercles and angles, and in the lumbar 

 region to the whole length of the transverse processes, and beyond these 

 to the lumbar fascia connected with them. 



e. The transversalis cervicis muscle prolongs upwards the column 

 of fibres of the longissimus dorsi. It arises from the internal tubercles 

 -of the transverse processes of the four or five highest dorsal vertebra?, 

 -and occasionally the last cervical, and is inserted into the ])osterior 

 tubercles of the transverse processes of five cervical vertebra? from the 

 second to the sixth inclusive. It ahvays receives a slip of the original 

 fibres of the longissimus dorsi. 



/. The trachelo-mastoid muscle, which may be regarded as the 



