This consists of two elongated symmetrical halves, the =rami=, which are united to one another at the median symphysis in front, while behind they diverge considerably, and each articulates with the glenoid surface of the corresponding squamosal. In young animals the rami are united at the symphysis by fibrous tissue, but in old animals they sometimes become fused together. The upper or alveolar border bears the teeth, and behind them is drawn out into a high laterally compressed =coronoid process= (fig. 72, 24), which is hollowed on its outer surface. Immediately behind the coronoid process is the transversely elongated =condyle= (fig. 72, 25), which fits into the glenoid cavity in such a way as to allow free up and down movement of the jaw, with but little rolling motion. The posterior end of the jaw below the condyle forms a short rounded process, the =angle= (fig. 72, 26). Two prominent foramina are to be seen in the lower jaw. These are firstly the =inferior dental foramen= (fig. 72, 28), which lies on the inner surface below the coronoid process; through it an artery and a branch of the fifth nerve enter to supply the teeth, and secondly the =mental foramen=, which lies on the outer side near the anterior end, and through which a branch of the same nerve emerges. (_c_) THE HYOID. The =Hyoid= of the dog consists of a transverse median piece, the =basi-hyal=[1] (fig. 72, 32), from which arise two pairs of =cornua=. The =anterior cornu= is much the longer of the two, and consists principally of three short separate ossifications, placed end to end and called respectively the =cerato-hyal=[143], =epi-hyal=, and =stylo-hyal=. All of them are short rods of bone, contracted in the middle, and expanded at the ends, where they are tipped with cartilage. The cerato-hyal (fig. 72, 31) lies next to the basi hyal. The stylo-hyal is terminated by a much smaller bone, the =tympano-hyal=, which lies in a canal between the tympanic and periotic, and is ankylosed to the periotic just to the anterior and inner side of the stylomastoid foramen. The =posterior cornu= of the hyoid is much smaller than the anterior; it consists of a short bone, the =thyro-hyal= (fig. 72, 33), which connects the basi-hyal with the thyroid cartilage of the larynx. FORAMINA OF THE SKULL. The foramina, or apertures perforating the walls of the skull, are very numerous, and may either be due to holes actually penetrating the bone, or may be small vacuities between the margins of two elsewhere contiguous bones. They may be divided into two groups, the first including I. The holes through which the =twelve cranial nerves= leave the cranial cavity. _a._ The most anterior of these nerves, the olfactory, leaves the skull by a number of small holes piercing the =cribriform plate= (fig. 72, 5).