280 FASCIA AND MUSCLES OF THE HORSE 
Origin.—The pelvic surface of the sacro-sciatic ligament near the ischiatic spine. 
Insertion.—The first four coccygeal vertebra and the coccygeal fascia. 
Action — Acting together, to de- 
press (flex) the tail, compressing it 
over the perineum; acting singly, 
to depress and incline it to the 
same side. 
Structure-—The origin of the 
muscle is aponeurotic. Becoming | 
fleshy, its fibers pass upward and _ 
backward and divide into two | 
layers. The lateral layer is at- | 
tached to the vertebre, the medial 
to the fascia; included between 
the two le the intertransversales. 
When the tail is raised, the ventral 
edges of the muscles produce a dis- 
tinct ridge at either side of the anus. 
Relations. —Laterally, the 
1,2: Branches oil lateral coceyeeul.vessclsandnerve: 3; sacro-sciatic ligament and the semi- 
dle coccygeal artery; 4, sacro-coceygeus dorsalis; 4’, sacro-cocey- yembranosus; medially,therectum 
geus lateralis; 5, 5’, intertransversales; 6, sacro-coccygeus ven- : Be 
ese 7 PSG asia GA CO ean, RoR and the sacro-coccygeus ventralis 
between fourth and fifth coceygeal vertebre. The veins are black. muscle. The internal pudic artery 
crosses the origin of the muscle. 
2. Sacro-coccygeus dorsalis (M. sacrococeygeus dorsalis medialis).'—This 
muscle lies along the dorso-median aspect of the tail, in contact with its fellow. 
Origin.—The last three sac- | 
ral spines and some of the cocecy- 
geal spines. 
Insertion.—The dorsal sur- 
face of the coccygeal vertebre. 
Action.—Acting together, to 
elevate (extend) the tail; acting 
singly, to elevate and incline it 
laterally. 
Structure—The muscle has 
a strong rounded belly. It is in- 
serted by means of short tendons 
which fuse with those of the next 
muscle. 
Relations.—Superficially, the 
coceygeal fascia; medially, its 
fellow; laterally, the sacro-cocey- 
geus lateralis; deeply, the verte- 
bree. 
Fig. 271.—Cross-secTion OF Tait oF Horse. 
3. Sacro-coccygeus lateralis 
(M. sacro-coecygeus dorsalis later- 
alis).-—This muscle hes immedi- 
ately lateral to the preceding. 
Origin.—The sides of the 
Fic. 272.—Musc ies oF PertneuM oF Horse. 
, 
a, Coceygeus; 6, retractor ani; c, c’, sphincter ani externus; 
é ‘Also termed the erector coccy- d, recto-coceygeus; e, sacro-coccygeus ventralis lateralis; f, retrac- 
fis. tor penis; g, bulbo-cavernosus; h, ischio-cavernosus; 7, internal 
2 Also known as the curvator pudie artery; & anus; J, penis. (After Ellenberger-Baum, Top. 
cocecygis. Anat. d. Pferdes.) 
