32 OUTLINES OF EQUINE ANATOMY. 



forward direction. Its superior margin anteriorly presents 

 a roughened prominence, to whicli the outer extremity of 

 the orbital process of os frontis is united. In front of 

 this, the inner surface, is concave, forming part of the orbit ; 

 the outer surface presents a squamous suture, terminating 

 anteriorly in a point for the zygomatic or malar bone. 

 The rest of the outer surface affords attachment to masseter 

 externus. The superior surface, at its junction with the 

 body, forms a deep, smooth, rounded groove, in which the 

 coracoid process of the inferior maxilla fits. The under 

 surface presents the glenoid cavity coate i with articular 

 cartilage, extending from without inwards on to the body, 

 rounded posteriorly by the mastoid process ; it articulates 

 with the condyle of the inferior maxilla through the medium 

 of a disc of cartilage. 



OS TEMPORAL PETROSTJM (Pair) is an extremely 

 irregular bone, wedged in between the occipital, parietal, 

 and squamous temporal bones. Its posterior surface lies in 

 contact with os occipitis, its anterior superior with the 

 parietal, inferiorly with the squamous temporal bone. It 

 is the hardest bone in the body, and co7itains the organ of 

 hearing (as will be afterwards described). Its inner sur- 

 face helps to form the inner surface of the cranium, and 

 presents digital impressions, with centrally /oramew audi- 

 torium internum. The external surface is very rough and 

 irregular ; superiorly it assists in forming the mastoid 

 ridge, giving attachments to several of the cervical muscles ; 

 centrally it presents the external auditory process, to 

 which the annular cartilage of the ear is attached, and 

 which is perforated by the external auditory hiatus, which 

 extends inwards as far as the tympanum. Below and in 

 front of this there is a prominence, which looks as if a 

 round peg had been driven into the bone ; this is the 

 hyoid process, to which the antero-superior angle of the 

 long cornu of os hyoides is united by fibro- cartilage. 

 Immediately below this is a rounded, roughened protu- 

 berance, denoting the situation of the mastoid cells inside 

 the bone ; hence it is termed the mastoid process. In front 

 of it is an elongated, sharp process, the styloid process, to 

 which tensor palati and stylo-pharyngeus are attached, and 

 just below and behind it is the styloid foramen, from which 

 the Eustachian tube passes to the pharynx. 



