ANATOMY OF THE HORSE. 21 



bone ; there are also several imperfect septa traversing the inte- 

 rior of each sinus, partially dividing it into as many different 

 chambers. 



Borders — Denticulated and squamous. The posterior or pa- 

 rietal is arched, describing segments of two distinct circles, one 

 running from within outwards, the other from above down- 

 wards, and is overlaid by the parietal and temporal bones. The 

 anterior or nasal border is waving, inclines backwards as well 

 as outwards, is terminated internally by the nasal process, and 

 is overlapped by the nasal and lachrymal bones. The frontal 

 border is straight ; broad and triangular anteriorly, where it 

 forms the septum between the sinuses : it unites with its fellow ; 

 and has at the place of junction, internally, a slighly elevated 

 longitudinal crest or spine, which with the opposite one forms a 

 groove for the reception of the longitudinal process of the dura 

 mater. The ethmoidal or outer border is irregular, forming a 

 junction with the lachrymal and sphenoidal, and, by overlap- 

 ping, with the ethmoidal bone. 



PARIETAL BOiNE. (OS PARIETALE.) 



Situation. Mesio-superior part of the cranium. 



Figure — Symmetrical; quadrilateral; vaulted: convex exter- 

 nally, concave internally. 



Division — Into two surfaces and four borders. 



T/ie External or Convex S^r/ace is divided longitudinally by a 

 mesian crest, which is bifurcated anteriorly and marks the course 

 of the suture existing in early life, into two lateral convexities ; 

 these are most elevated towards the supero-external angles, and 

 their surfaces, though otherwise smooth, exhibit a few scattered 

 small foramina, and are imprinted by the continual action of the 

 muscles covering them, the prints growing deeper with age ; 

 and, it appears, the general prominence less. The triangular 

 space between the bifurcations of the crest generally rises above 

 the level of the surrounding surface. 



The Diternctior Concave Surface is divided into two concavities 

 by an internal crest which is commonly double, havino- a longi- 

 tudinal groove in* the middle : it is terminated posteriorly by a 

 three-sided process, the parietal protuberance, to which, as well 

 as to the crest itself, is attached the falciform process of the 

 dura mater. In front of this projection the longitudinal furrow 

 ends in the two transverse grooves, which run along the poste- 

 rior border, between it and the temporal bones : the former 

 lodges the longitudinal, the latter the lateral sinuses of the dura 

 mater. The cavities themselves are adapted to cover the mid- 



