A broad, triangular, fiat muscle, situated on the side of the neck, and extending from the summit of the head backward to the withers.

Origin. - From the superior spinous processes of the 2nd, 3rd, and 4th dorsal vertebrae and the upper border of the ligamentum nucha?.

Insertion. - Into the mastoid crest of the temporal bone and the transverse processes of the first five cervical vertebrae.

Action. - Acting alone, the splenius draws the head and neck towards the side upon which it acts. When co-operating with its fellow on the opposite side, they elevate the head and neck.