372 



BACK. 



sidered distinct muscles. They are inseparable 

 below ; their structure, direction, and uses are 

 alike ; and they are inserted similarly the one 

 into transverse processes, the other into a part 

 of the cranium perfectly analogous. 



The splenii cover the longissimus dorsi, 

 the complexus, the transversalis colli, and the 

 trachelo-mastoideus. The splenii of opposite 

 sides pass off from each other as they ascend, 

 leaving a triangular space at the upper part of 

 the neck, in which the complex! appear. 



The action of these muscles is to incline the 

 head to one side, and rotate it. If the sterno- 

 mastoideus of the same side act with them, the 

 head is inclined directly to the shoulder. If 

 the splenii of opposite sides act together, the 

 head and neck are kept erect, and in this they 

 are assisted by the complexus and trapezius. 

 They strap down the deeper muscles. Their 

 name is said to be derived from some resem- 

 blance to the spleen! (Turtorfs Glossary.) 



The splenii are generally better marked in 

 other mammalia than in man. In the mole 

 they are particularly strong. In carnivora 

 there is no splenius colli. In the horse the 

 splenius capitis is inserted into the mastoid 

 process by a tendon common to it and to the 

 trachelo-mastoideus. Birds have no splenius. 

 Reptiles have analogous muscles; but fish 

 have not. 



Fifth layer. On removing the splenii and 

 all those previously described, we expose the 

 Jift/i layer of muscles, consisting of the sacro- 

 lumbahs, longissimus dorsi, spinalis and semi- 

 spinalis dorsi, cervicalis descendens, trans- 

 versalis colli, traehelo-mastoideus, and com- 

 plexus. These, excepting the last, are long 

 and slender, quite different from those hitherto 

 described. They are also less distinct from 

 each other. The first four of them fill up the 

 vertebral groove from the sacrum to the neck, 

 and might well be considered as one muscle 

 the erector spirits. 



The sacro-lumbalis y placed most externally, 

 arises from the posterior surface of the sacrum, 

 from the margin of the ilium where the latter 

 overlaps the former, from the sacro-iliac liga- 

 ments, and from the extremities of the trans- 

 verse processes of the lumbar vertebrae ; pas- 

 sing upwards, and tapering in form, it is in- 

 serted by tendinous slips into the angles of all 

 the ribs. It is reinforced in its ascent by acces- 

 sory fibres (musculi accessor ii), which arise at 

 the upper margins of the five or six lowest true 

 ribs, internal to their angles, run upwards and 

 outwards over one or two intercostal spaces 

 under cover of the longer fibres, and are in- 

 serted with them into the angles of the ribs. 

 These accessory fibres constitute almost the 

 entire of the muscle at its upper part. 



The longissimus dorsi, placed along its inner 

 side, arises from the spinous and transverse 

 processes of the lumbar vertebrae, and from the 

 spines of the sacrum and its posterior surface 

 down to its apex. It forms a thick, somewhat 

 square, mass in the loins ; on the dorsum it 

 becomes fiat and tapering, and ends in a point 

 at the top of the thorax. It is inserted by two 

 rows of tendinous and fleshy slips one row 



into the transverse processes of all the dorsal 

 vertebrae, the other row, externally, into the 

 lower edge of the ribs near their articulations 

 with those processes. The costal slips are 

 seldom inserted into all the ribs, the first two 

 or three and the last two or three being often 

 without them. 



The posterior surface of these two rmiscles 

 consists below of a strong tendinous layer, from 

 which a great part of their fleshy fibres arises ; 

 it is common to the two as far as the middle 

 of the lumbar region ; there it terminates on 

 the sacro-lumbalis, but ascends much higher on 

 the longissimus dorsi, separating into several 

 distinct bands, between which vessels and 

 nerves come out. 



This tendon is not to be confounded with 

 the fascia lumborum, which is much thinner 

 and adheres to its posterior surface. 



The spinalis dorsi* lies close along the spi- 

 nous ridge, arising from the two superior lum- 

 bar, and three inferior dorsal spines. It forms 

 a thin muscle and is inserted into the nine 

 superior dorsal spines. Below it is in contact 

 with the longissimus; above it is separated 

 from it by the next muscle. 



The semi-spinalis dorsi arises from the trans- 

 verse processes of the dorsal vertebrae from the 

 eleventh to the sixth inclusive by so many 

 distinct tendinous fasciculi which pass up, be- 

 come fleshy, unite and are inserted into the 

 spines of the four or five superior dorsal and 

 two inferior cervical vertebra. The name of 

 this muscle is intended to denote its attachment 

 to the transverse as well as to the spinous pro- 

 cesses. It is at first concealed by the longis- 

 simus dorsi, then lies along the inner side of 

 that muscle and the outer side of the spinalis 

 dorsi, with which last it is often united in 

 description. 



These four muscles elevate the spine, and 

 give it an inclination to their own side. 

 The sacro-lumbalis will also depress the ribs 

 slightly. 



The cervicalis descendens looks like a con- 

 tinuation of the sacrolumbalis, between which 

 and the longissimus dorsi it arises. Its origin 

 is by tendinous slips from the angles of the 

 second, third, fourth, fifth, and sixth ribs. 

 These are at first blended with those of the 

 sacro-lumbalis ; then they unite and form a 

 slender muscle, which runs upwards, out- 

 wards, and forwards, to be inserted into the 

 transverse processes of the third, fourth, fifth, 

 and sixth cervical vertebrae, between the trans- 

 versalis eolli and the levator anguli scapulae. 



This muscle may elevate the ribs or extend 

 the neck, turning it to one side. It is often 

 considered as a portion of the sacro-lumbalis, 

 and sometimes called musculus accessorius, 

 or cervicalis ascendens. The name cervicalis 

 descendens, that by which it is best known, was 

 given to it by Diemerbroeck, who described 



* Under the denominations transversaire epineux, 

 which may be latinized transversus spines, Bichat 

 and some other continental anatomists include the 

 spinalis dorsi, semi-spinalis dorsi, spinalis coUi, and 

 mvltifidus spinee. ED. 



