186 OUTLINES OF EQUINE ANATOMY. 



Semispinales colli, dor si, et lumborum, wliicli com- 

 mences at the superior spinous process of the dentata and 

 extends to the sacrum. It is composed of a chain of muscu- 

 lar fasciculi, which run obliquely downwards and bachwards 

 from the superior spinous processes of the vertebrae to the 

 oblique processes of the vertebrae posteriorly placed to these, 

 sometimes passing over two or three prior to insertion. A 

 somewhat similar muscle is 



Intertransversales colli, dorsi, et lumborum, which is 

 composed of a series of fasciculi, which in the neck are 

 situated between the transverse processes of the vertebrae, 

 in the back are blended with levatores costarum, and in the 

 loins are found between the transverse processes. 



Levatores costarum are a series of small triangular 

 muscles arising from the transverse processes of the dorsal 

 vertebrae, and running to the anterior border and external 

 surface of the ribs as high up as their necks ; superiorly 

 they blend with intertransversales dorsi, and they are 

 merely the superior parts of the 



Intercostales externi, which consist of muscular and ten- 

 dinous fibre intermixed, which run obliquely downwards 

 and backwards from the posterior margin of one rib to the 

 anterior margin of the rib immediately posterior to it. 

 They extend no lower than the inferior extremities of the 

 ribs, for between the cartilages the 



Intercostales interni fill the intervening spaces with 

 fibres running obhquely downwards and forwards. Those 

 portions of these muscles situated between the sterno- 

 costal cartilages (which are attached inf eriorly to the lateral 

 parts of the sternum) are termed sterno-costales externi. 

 From this point upwards we see the internal intercostals 

 situated internally to the external intercostals, the artery, 

 vein, and nen^e being, during a considerable part of their 

 course, between the two muscular layers thus formed. The 

 pleura costalis covers the inner surface of the internal 

 intercostals. 



The source of the intercostal arteries has been already in- 

 dicated. From their origin they run over the lateral part 

 of the bodies of the dorsal vertebrae, giving off medullary 

 tranches to these bones ; of those intercostals which arise 

 from the posterior aorta the right are somewhat the longest, 

 and before reaching the intercostal spaces pass above the 

 thoracic duct and vena azygos. In passing the interver- 



