_Relations._--Outer surface with the splenius (Fig. 73, _b_), complexus (Fig. 69, _b_), and longissimus capitis (Fig. 73, _g_). Inner surface with the obliquus inferior (Fig. 71, _b_), the wing of the atlas, and the rectus lateralis (Fig. 72, _d_). Ventral border with the cleidomastoid (Fig. 73, _d_) and one head of the levator scapulæ ventralis (Fig. 72, _c′_). _Action._--Flexes the head laterally. =Mm. interspinales= and =intertransversarii= are found in the neck region also; they are described with the muscles of the back. C. MUSCLES OF THE TAIL.--=M. extensor caudæ medialis= (Fig. 70, _e_).--This is a continuation caudad of the multifidus spinæ (Fig. 70, _d_); it lies next to the dorsal median line, the muscles of right and left side touching one another in the middle line. _Origin_ by numerous fleshy bundles from the spinous processes of the sacral and first caudal vertebræ. The fibres pass caudad and are inserted by tendons into the articular processes and the dorsal surface of the caudal vertebræ. _Action._--Extends (raises) the tail. =M. extensor caudæ lateralis= (Fig. 70, _f_).--This is a continuation caudad of the medial portion of the longissimus dorsi (Fig. 70, _a_); it lies just laterad of the extensor caudæ medialis (Fig. 70, _e_). _Origin_ in many fleshy bundles from the articular processes of the sacral vertebræ, and the transverse processes of the caudal vertebræ. The fibres curve dorsocaudad and are inserted by many long slender tendons on the dorsal surfaces of the caudal vertebræ. The muscle grows continually smaller as it passes caudad. _Action._--Raises the tail. =M. abductor caudæ= (coccygis) =externus= (Fig. 68, _w_; Fig. 70, _g_).--A rounded muscle on the lateral surface of the cranial part of the tail. _Origin_ from the medial side of the dorsal border of the ilium, and from the dorsal surface of the sacrum. The muscle passes caudad, lying just ventrad of the extensor lateralis, and is _inserted_ into the transverse processes and lateral surfaces of the caudal vertebræ, as far back as the eighth or ninth. _Action._--Bends the tail sideways. =M. abductor caudæ internus= (or M. coccygeus).--A large flat muscle, having origin on the spine of the ischium. The muscle passes dorsomediad, spreading out, and is inserted into the transverse processes of the second to the fourth caudal vertebræ. _Relations._--Lateral surface with the caudofemoralis (Fig. 68, _s_), gluteus maximus, and pyriformis. Medial surface with the iliocaudalis and the flexor caudæ longus (Fig. 68, _x_). =M. iliocaudalis= (Str.-D.) (Fig. 162, 11′, page 398).--This represents a portion of the levator ani of man, and in some specimens is united with that muscle (Fig. 162, 11) in the cat. _Origin_ along the ventral half of the medial surface of the ilium, caudad of the sacrum. The fibres pass caudad and are _inserted_ by a flat tendon into the ventral surface of the caudal vertebræ, from the second or third to about the seventh.