260 THE MUSCLES. 



Spinal Region of the Back and Loins. 



This offers for study seven pairs of muscles, nearly all of which have their 

 insertions extended over the dorso-lumbar spine, and are disposed in four layers 

 on each side of this long multifidious crest. These muscles are — 



In the First Layer. 

 Trapezius. Latissimus Dorsi. 



In the Second Layeb. 

 S&rratm Anticus. Serratus Posticus. 



In the Third Layer. 

 Longissimus Dorsi. Transversalis Costarum. 



In the Fourth Layer. 

 Semispinalis of Back and Loins. 



Preparation. — 1. Place the animnl in the second position. 2. Remove the skin with the 

 panniculus and the mass of olecranian muscles, to show, in a first operation, the trapezius and 

 latissimus dorsi (Fig. 159). 3. In a second operation, remove the entire fore limb, with 

 the latissimus dorsi muscle, the mode of termination of which may then be studied ; then pre- 

 pare the two smiU serrated muscles. 4. Remove thvse two muscles, as well as the angularis 

 of the scapula and the splenius, to expose the transversalis costarum and longissimus dorsi 

 (Fig. 163). The superior brancli of the latter remaining covered by the great complexus, 

 excise tliis muscle, leaving only its insertions into the transverse processes of the dor.-al 

 vertebrje, to show liow they are fixed between the two branches of the longissimus dorsi. 5. 

 Dissect the semispinalis by removing the longissimus dorsi and the internal angle of the ilium. 



First Layer. 



1. Trapezius (Fig. 159, 1, 3). 



Synonym. — Dorso- and cervico-acromialis — Girard. 



Situation — Form — Stnuiure. — ^This is a superficial membraneous muscle, 

 situated on the sides of the neck and withers. Its shape is that of a triangle 

 base upwards. It is aponeurotic at its upper border and in its centre, which 

 allows it to be distinguished, especially in emaciated subjects, into a cervical and 

 a dorsal portion. The fleshy fibres of the first are directed do-miwards and back- 

 wards ; those of the second are oblique forwards. 



Attachments. — By its superior aponeurosis, it is fixed to the cord of the cer- 

 vical ligament and to the summits of the transverse processes of the first dorsal 

 vertebrJE, where it adheres to the external face of the latissimus dorsi. By its 

 central aponeurosis and that of its summit, it is attached to the tuberosity of the 

 olecranian spine and the external scapular aponeurosis. 



Relations. — This muscle is covered by two aponeurotic planes, the fibres of 

 which cross its own at a right angle. Inwardly, it responds to the rhom- 

 boideus, splenius, angularis, deep pectoral, the supra- and infra-spinatus, and 

 the latissimus dorsi. 



Action. — It raises the shoulder, and carries it forward or backward, according 

 as one or other of its muscular portions contract. 



2. Great Dorsal (Latissimus Dorsi) (Fig. 159, 2). 



Synonyms. — Dorso-humeralis — Girard. (Latissimus dorsi — PercivaU. ) 

 Form — Situation — Structure — Attachments. — A very broad triangular muscle,' 



