TEE HEAD. 47 



and an internal face, and a circumference which brings it into contact with the 

 adjoining cranial bones ; the latter is subdivided into two anterior lateral borders, 

 two posterior lateral borders, an anterior and posterior salient angle, and two 

 lateral re-entering angles. 



Faces. — The external face is divided into three portions by the double flexure 

 of the bone : one looks forward, another upward, and the third backward. It 

 exhibits: — 1. On the median line, and from before to behind : a, an antero- 

 posterior ridge which constitutes the origin of the parietal ridges, to be mentioned 

 hereafter ; b, a transverse, voluminous, and very prominent eminence, marked 

 posteriorly by deep imprints, with a medium projection named the cervical 

 tuberosity ; this is the external occipital tuberosity which, in the Horse, corre- 

 sponds at the same time to the superior curved lines of the occipital bone of Man. 

 This protuberance forms the culminating point of the head, and divides the 

 anterior and superior parts of the external face of the bone ; c, the occipital 

 foramen {foramen magnum), a large orifice that passes through the bone at the 

 posterior flexure, and establishes a communication between the cranial cavity and 

 spinal canal : d, the external surface of the basilar process — a narrow and thick 

 prolongation formed by the bone as it passes to meet the sphenoid : this surface 

 is convex laterally. 2. On the sides : a, A sharp crest which prolongs, laterally, 

 the superior curved lines, and descends on the middle of the lateral anterior 

 border, to be continued with the superior root of the zygomatic process and the 

 mastoid crest of the temporal bone ; b, Linear imprints, parallel to the latter, 

 and prolonged on the base of the styloid process : they are destined for the 

 insertion of the small oblique muscle of the head, and represent the inferior 

 curved lines of the occipital bone of Man ; c, Within these imprints is a shghtly 

 roughened cavity for the insertion of the posterior recti muscles ; d, The two 

 condyles — articular eminences with a double convexity, one superior, the other 

 inferior : these eminences are situated on each side of the occipital foramen 

 {foramen magnum), and correspond to the anterior cavities of the atlas ; e. More 

 outwards are the two styloid {paroccipital) processes, or jugular eminences — long 

 projections flattened on each side, terminated in blunt points, directed backwards, 

 and separated from the condyles by a deep space, the stylo-condyloid notch ; f 

 Under the condyles is the condyloid fossa — a smooth depression, pierced at the 

 bottom by the condyloid foramen, which penetrates the cranium. 



The internal face of the occipital bone is concave, and shows : behind, the 

 foramen magnum ; above, an uneven surface, which forms the roof of the 

 cerebral cavity ; below, the superior face of the basilar process, slightly hollowed 

 into a groove ; on the sides, the internal orifice of the condyloid foramen. 



Circumference. — The anterior lateral borders are thick, and are united by 

 suture with the parietal bone, and with the tuberous portion of the temporal 

 bone by the harmonia suture. The posterior lateral borders are sharp, and 

 constitute the sides of the basilar process ; each concurs in the formation of the 

 occipito-spiheno-temporal hiatus, also termed the foramen lacerum basis cranii — a vast 

 irregular opening, extending from above downwards, penetrating the cranium, and 

 divided by a ligament, in the fresh state, into two portions, one inferior, the 

 anterior foramen lacerum, the other superior, the jjosterior foramen lacerum. The 

 anterior angle, which is dentated, is dovetailed into the parietal bone. The posterior 

 angle is very thick, and forms the summit of the basilar process ; it is united by 

 suture with the body of the splienoid. The lateral re-entering angles, or jugular 

 notches, correspond to the point where the bone is bent posteriorly ; they separate 



