TRACHELO-MASTOID— SPINALIS DORSI 419 



Origin. — The back of the transverse processes of tlie five or six upper thoracic 

 vertehra'. internal to the insertion of tlie jjreceding nuiscle. 



Insertion. — The posterior tubercles of the transverse processes of the second 

 to the sixth cervical vertebrtX3. 



7. TRACHELO-MASTOID 



The trachelo-mastoid — named from its origin, part of which is in the neck 

 (zpd/rjAoq)^ and its insertion ujjon the mastoid process — is a similar but smaller 

 inusculo-tendinous band. 



Origin, — (1) The back of the articular processes of the lower three or four 

 cervical verte])ra3; (2) the back of the transverse jsrocesses of the four or five upper 

 thoracic vertelira?. 



Insertion. — The posterior l)order of the mastoid process. 



Structure of the middle division. — The three parts of this division have a 

 close connection with one another, and a long tendinous expansion wliich covers 

 the inner and back part of the longissimus clorsi, is common to it and the spinalis 

 dorsi. 



The association of the two upper portions of the division is so close that they 

 are sometimes described together under the name transversalis, the trachelo-mastoid 

 being called the transversalis capitis to distinguish it from that part of the muscle 

 which is inserted into the neck. All the upper Elements of this long compound 

 muscle have tendinous origins and insertions. 



The trachelo-mastoid portion is often found to have a tendinous intersection 

 crossing its fleshy fibres. 



Nerve-supply. — The external division of the jiosterior branches of the lower 

 cervical, all the thoracic, and the upper lumbar ner\'es. 



Action. — (1) To extend the cervical, thoracic, and lumbar spine; (2) to flex it 

 laterally; (3) to extend and laterally flex the head, rotating the face to the same 

 side. 



Relations. — Superficially, it is covered by the latissimus dorsi, trapezius, rhom- 

 boidei, serratus posticus inferior and superior, and the two splenii; upon its inner 

 border lie the spinalis dorsi and complexus. Upon its outer lie the muscles of the 

 outer division and the external divisions of the posterior branches of the spinal 

 nerves. Beneath lie the multifidus spinas and the semispinales dorsi et colli. 



Inner Division 



The inner division consists usually of a single muscle, the spinalis dorsi; but 

 sometimes a small muscle, the spinalis colli, continues the series into the neck. 



8. SPINALIS DOPxSI 



The spinalis dorsi — named from its attachment to the spines in the dorsal 

 region — is a musculo-tendinous band closely connected below with the aponeurosis 

 on the back of the longissimus dorsi. 



Origin. — The erector spinse, and esjiecially that ])art which is attached to the 

 two or three lower thoracic and the upper lumbar spines. 



Insertion. — The spines of the upper thoracic vertebra^. 



Structure. — L"i)on its i)osterior surface it is covered l)y a thick ai)oneurosis, 

 from the upper edge and anterior surface of which fleshy fil:)res i)ass almost directly 

 upwards, and are then inserted by means of four to eight tendons into as many of 

 the upper thoracic spines. They are closely blended with the tendons of the semi- 

 spinalis dorsi at their insertion. 



Nerve-supply. — The posterior branches of the thoracic nerves. 



Action.— To extend the thoracic spine. 



