([Fig. 38] and [Fig. 104]).—The hyoid bone forms the support for the tongue and gives origin to muscles passing to the tongue and larynx. It also supports the thyroid cartilage ([Fig. 104], 1).

[Fig. 38].—Hyoid Bone, Dorsal View.

a, body; b, c, d, e, cranial cornu; f, caudal cornu; b, ceratohyal; c, epihyal; d, stylohyal; e, tympanohyal; f, thyrohyal.

It consists of a transverse bony bar, the body ([Fig. 38], a) and of two cornua or horns attached to each end of the body.

The cranial cornu (lesser cornu of human anatomy) is the longer ([Fig. 38], b-e). Each arises from the cranial face of the body at its lateral end, curves laterad, and then caudodorsad. It consists of four bony pieces movably united by cartilage.

The terminal piece is the tympanohyal (e); it is imbedded in the tympanic bulla just ventrad of the stylomastoid foramen. It is not therefore seen attached to the cornu after the latter has been separated from the skull. The other pieces become successively shorter toward the body, and are called stylohyal (d), epihyal (c), and ceratohyal (b).

The caudal cornua (f) (greater cornua of human anatomy) arise from the ends of the body. Each consists of a single piece of bone, the thyrohyal (f), which passes caudolaterad; its free end is united to a process of the thyroid cartilage ([Fig. 104], 1).

The Skull as a Whole.

—In the following description of the skull as a whole the mandible, hyoid, and ear-bones are not included.