276 FASCIiE AND MUSCLES OF THE HORSE 



Insertion.— The occipital bone, below the complexus; the tendon of insertion 

 of the complexus. 



Action. — To extend the head. 



Structure. — The muscle is fleshy and may be divided into two parallel parts, 

 superficial and deep. The former blends somewhat with the terminal part of the 

 complexus. The deep part may be termed the rectus capitis dorsalis medius. 

 Bundles frequently arise from the fascia over the obliquus capitis posterior. 



Relations. — Superficially, the obliquus capitis anterior, splenius, and com- 

 plexus; medially, the ligamentum nuchje; deeply, the atlas, the atlanto-occipital 

 articulation, and the rectus capitis dorsahs minor. The dorsal branch of the first 

 cervical nerve appears between this muscle and the obliquus capitis anterior. 



Blood-supply. — Occipital artery. 



Nerve-supply. — Dorsal branch of the first cervical nerve. 



12. Rectus capitis dorsalis minor. — This small muscle lies under cover of the 

 preceding. 



Origin. — The dorsal surface of the atlas. 



Insertion. — The occipital bone beneath the preceding muscle and lateral to the 

 funicular part of the ligamentum nuchae. 



Action. — To assist the preceding muscle. 



Structure. — It is fleshy and varies a good deal in volume, being sometimes 

 small and difficult to recognize.^ On the other hand, it is sometimes double. 



Relations. — Superficially, the preceding muscle and the obliquus capitis an- 

 terior; deeply, the atlas and the atlanto-occipital articulation. 



Blood-supply. — Occipital artery. 



Nerve-supply. — Dorsal branch of the first cervical nerve. 



The Fascle and Muscles of the Back and Loins 

 (fascls: et musculi dorsi et lumborum) 



The superficial fascia presents no special features. The lumbo-dorsal fascia 



(Fascia lumbo-dorsalis) closely invests the muscles, but is easily stripped off the 

 longissimus. It is attached medially to the supraspinous ligament and the spinous 

 processes of the vertebrse; it divides laterally into two layers. The superficial 

 layer is practically the aponeurosis of the latissimus dorsi. The deep layer gives 

 origin to the serratus dorsalis, the lumbar part of the obliquus abdominis externus, 

 the transversus abdominis, and the retractor costae. Its lateral edge curves under 

 the longissimus and is attached to the ribs and lumbar transverse processes. Pos- 

 teriorly it is continuous with the gluteal fascia. At the withers it forms an impor- 

 tant structure, the dorso-scapular ligament. This is a strong tendinous sheet, 

 attached to the third, fourth, and fifth thoracic spines. Its upper part is very 

 thick and gives origin bj^ its superficial surface to the rhomboideus thoracalis, by 

 its anterior part to the splenius. The lower part is thin and elastic, and furnishes 

 numerous lamellae which intersect the scapular part of the serratus ventralis and 

 are attached to the scapula. Three lamellae are detached from the ligament. 

 The deepest of these passes between the longissimus and spinalis and is attached to 

 the transverse processes of the first seven thoracic vertebrae; it gives attachment 

 to the complexus. The middle one dips in between the longissimus dorsi and 

 longissimus costarum. The superficial one gives origin to the serratus dorsalis. 

 A strong fascial layer, the ilio-lumbar ligament, extends from the last rib to the 

 tuber coxae. 



There are nine pairs of muscles in this region, arranged in four layers. 



1 This seems due to pressure produced by pathological changes in the supra-atloid bursa, 

 which are frequently extensive in dissecting-room subjects. 



