THE SKELETON OF THE DOG. THE SKULL. 399 



a short rounded process, the angle (fig. 72, 26). Two promi- 

 nent 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 1 , 

 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, 3 1 ) 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, arid 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. 



1 These are not strictly homologous with the basi-hyal and cerato-hyal 

 of the Dogfish. 



