DORSO-LUMBAR REGION. 199 



Relation. Externally with the superficial costarum, and 

 gluteus maximus which overlaps it in the lumbar region ; in- 

 feriorly with the transversalis costarum ; internally with the ribs, 

 vertebras, and semispinalis dorsi et lumborum ; anteriorly with 

 the spinalis dorsi. 



Action. It is brought powerfully into play in kicking and 

 rearing, by elevating the fore or hind quarters, according to 

 whether the fore or hind limbs are fixed. Acting singly, the 

 result is lateral flexion of the back and loins. It may assist also 

 in expiration. 



SPINALIS DORSI.* 



Situated deeply on the withers, it is pyramidal in form, 

 aponeurotic at its origin, with a fleshy belly ; it is with difficulty 

 separated from the longissimus dorsi. 



Origin. By aponeurosis from the supraspinous ligament, as 

 far back as the twelfth, and from the posterior borders of the 

 spinous processes of the six anterior dorsal vertebrae. 



Insertion. To the superior spinous processes of the last three 

 or four cervical vertebrae. 



Relation. Externally with the trapezius and rhomboideus 

 brevis ; anteriorly with the complexus major and splenius ; infe- 

 riorly with the longissimus dorsi ; internally with its fellow, the 

 ligamentum nuchae, the anterior dorsal vertebras, and semispinalis 

 dorsi. 



Action. To assist in elevating the neck. 



SEMISPIXALIS DORSI ET LUMBORUM. 

 (Spinalis Transversus.) 



In contact with the dorsal and lumbar spines, this muscle con- 

 sists of a number of fasciculi, whose fibres are directed upwards 

 and forwards. 



Origin. From the sacrum, the oblique processes of all the 

 lumbar, and transverse processes of all the dorsal vertebrae. 



Insertion. The spinous processes of the vertebras, the 

 fasciculi each passing over two or three spines before being 

 inserted ; it becomes continuous with the spinalis colli at the 

 seventh cervical. 



* [This muscle may be regarded as part of the longissimus dorsi ED.] 



