34 TEE BONMS. 



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; 6, 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 pro- 

 tuberance which, in the Horse, corresponds 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 oriiice that passes through the bone at the posterior flexure, and esta- 

 blishes 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 slightly- 

 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 processes, or jugular eminences, long 

 projections flattened on each side, terminated in blunt points, directed back- 

 wards, and separated from the condyles by a deep space, the stylo-condyloii. 

 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. f 



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

 suture with the parietal bone, and mth the tuberous portion of the tem-^^aral 

 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-spleno-temporal hiatus, also termed the lacerated foramen, a vast 

 irregular opening, extending from above downwards, penetrating the 

 cranium, and divided by a ligament, in the fresh state, into two portions, 

 one mferior, the anterior lacerated foramen, the other superior * the posterior 

 lacerated foramen. The anterior angle, which is dentated, is dovetailed into 

 the parietal bone. The posterior angle is very thick, and forms the summit 

 ot the basilar process; it is united by suture with the body of the 

 sphenoid. The lateral re-entering angles, or jugular notches, correspond to the 



' (The Tiarmonia suture (&p,7v, to adapt) is the simple apposition of contiguous borders, ■ 

 which are roughened to facilitate retention.) r 1 1 b uo uuiu , 



' (The anterior and posterior lacerated foramen of Man.) 



