THE MUSCLES OF THE THORAX 281 
sacral spines, with the multifidus, and the transverse processes of the sacral and 
coceygeal vertebre. 
Insertion —The lateral surface of the coccygeal vertebre, except the first four. 
Action.—Acting with its fellow, to assist the preceding muscle in elevating the 
tail; acting singly, to incline it to the same side. 
Structure-—This muscle appears to be a direct continuation of the multifidus 
dorsi. The belly is fusiform and receives reinforcing fasciculi from the transverse 
processes of the sacrum. This is succeeded by bundles of tendons, as many as four 
lying alongside of each other. 
Relations.—Superficially, the lateral sacro-iliac ligament and the coccygeal 
fascia; dorsally, the sacro-coccygeus dorsalis; ventrally, the intertransversales; 
deeply, the vertebre and a branch of the lateral coccygeal artery and accompanying 
vein and nerve. 
4. Intertransversales caude (Mm. intertransversarii caudw#)—These con- 
sist of muscular bundles which lie on the lateral aspect of the tail, between the 
preceding muscle and the sacro-coccygeus ventralis. They begin on the lateral 
edge of the sacrum and occupy thespaces between the transverse processes, to which 
they are attached. They are, however, not arranged in a strict segmental manner. 
Action.—Acting together, to fix the coccygeal vertebre; acting singly, to assist 
in lateral flexion. 
5. Sacro-coccygeus ventralis (Mm. sacro-coceygei ventrales)..—This muscle 
lies on the ventral aspect of the sacrum and coccyx. It is composed of two parts, 
described by Bourgelat and the German anatomists as separate muscles. 
(a) The lateral part (M. coccygeus ventralis lateralis) is much the larger of 
the two. It arises from the lateral part of the ventral surface of the sacrum, about 
as far forward as the third foramen, and is inserted into the transverse processes 
and ventral surface of the coccygeal vertebre. 
(b) The medial part (M. sacro-coccygeus ventralis medialis) arises from the 
ventral surface of the sacrum medial to the preceding muscle and the first eight 
coccygeal vertebre, and is inserted into the ventral surfaces of the coccygeal ver- 
tebre. 
Action —Acting together, to depress (flex) the tail; acting singly, to incline 
it laterally also. 
Structure—The lateral part has a somewhat compressed belly, and receives 
bundles from the transverse processes of the coccygeal vertebre. The medial part 
is much smaller and shorter, reaching only about to the middle of the tail. 
Relations.—Ventrally, the pelvic and coccygeal fasciz; dorsally, the sacrum, 
coccygeal vertebre, and the intertransversales; laterally, the sacro-sciatic liga- 
ment, the coccygeus, and the coccygeal fascia; medially, its fellow, the recto- 
coecygeus, and the middle coccygeal vessels. Branches of the lateral coccygeal 
vessels and nerves lie between the lateral division of the muscle and the intertrans- 
versales. 
Blood-supply—Miiddle and lateral coccygeal arteries. 
Nerve-supply.—Coccygeal nerves. 
THE MUSCLES OF THE THORAX 
(MUSCULI THORACIS) 
These consists of seven muscles or sets of muscles, which are attached to the 
thoracic vertebrz, to the ribs and their cartilages, and to the sternum. They are 
muscles of respiration. 
1. Levatores costarum.—These constitute a series of small muscles which oc- 
cupy and overlie the dorsal ends of the intercostal spaces. 
1 Also known as the depressor coccygis. 
