CRANIUM. 



739 



rence, by a line passing on each side along 

 the outer border of the orbitar process of the 

 frontal bone, the junction of the parietal and 

 sphenoid; the parietal and temporal bones; and 

 the lateral limb of the internal crucial spine of 

 the occipital. 



It is placed obliquely downwards and back- 

 wards, and consists of three principal divisions 

 or platforms the posterior being the lowest, 

 the anterior the highest ; and the middle, on a 

 plane between the two. 



The anterior division is called the anterior 

 fossff, and sustains the anterior lobes of the 

 brain. It is concave in the middle and con- 

 vex on each side ; it is limited, anteriorly by 

 the merging of the orbitar processes into the 

 general mass of the frontal bone, and poste- 

 riorly by the posterior margin of the alae mi- 

 nores. On the median line, from before back- 

 wards, we encounter the foramen ccecum ; the 

 crista galli; the ethmoidal process of the 

 sphenoid bone ; and, lastly, the smooth sur- 

 face of that bone on which the olfactory nerves 

 repose. On either side of the crista galli is 

 the processus cribrosus, with its foramina, and 

 slit for the ethmoidal nerve and vessels ; more 

 outwardly, is the transverse suture uniting this 

 process to the frontal bone, and in it may be 

 seen the internal orifice of the anterior internal 

 orbitar foramen. From hence outwards, is the 

 orbitar process of the frontal bone, somewhat 

 arched, and displaying, more evidently than 

 in the rest of the skull, the digital impressions 

 of the brain ; behind this is the transverse 

 suture uniting it to the small wings of the 

 sphenoid bone ; and, lastly, there is the upper 

 surface of the small wings themselves. 



The middle fossa consist of two large fossae 

 laterally, and one, which is smaller, centrally. 

 This latter is the pituitary fossa; in its front 

 is the olivary, and, behind it, is the basilar 

 process ; on its sides are the sulci carotici, and 

 its corners are bounded by the ephippial or 

 clinoid processes. In front of the olivary 

 process is the groove on which the optic nerves 

 decussate; and between it and the anterior 

 ephippial processes of each side is the foramen 

 opticum. 



The lateral fossae are very deep and of an 

 irregular triangular figure, the base of which 

 is directed outwards. Anteriorly they are 

 bounded by the small wings of the sphenoid 

 bone, and posteriorly by the ridge which se- 

 parates the cerebral from the cerebellar surface 

 of the petrous portion of the temporal bone. 

 Each is formed, anteriorly and internally, by 

 the great wing of the sphenoid ; posteriorly, 

 by the cerebral surface of the petrous process ; 

 and, externally, by the squamous process of 

 the temporal bone. In it are seen the lines of 

 junction between these parts, and the sulci 

 formed by the spinous artery of the dura rnater. 

 At its anterior boundary there is the foramen 

 lacerum orbitale superius; and behind it, 

 inclining gradually outwards, there are in suc- 

 cession, the foramen rotundum, the foramen 

 ovale, the foramen spinale, the sulcus Vidi- 

 anus, the hiatus Fallopii, the depression for 



the Glasserian ganglion, and the processus semi- 

 circularis. To the inner side of this range, 

 and on a level with the foramen ovale, is the 

 foramen lacerum anterius. 



The posterior division extends from the 

 basilar process of the sphenoid bone to the 

 internal tubercle of the occiput. Its margin 

 is of a triangular figure, with its base curved 

 and directed backwards. The petrosal ridges 

 form the sides of the triangle, and the lateral 

 limbs of the internal crucial spine, its base. 

 On the median line and passing backwards 

 we observe the superior sulcated surface of the 

 basilar process, with a groove on each side for 

 the basilar sinus ; the foramen magnum with 

 the anterior condyloid foramina near its ante- 

 rior part ; and, lastly, the inferior limb of the 

 internal crucial spine, separating the two 

 great cerebellar fossae. Each of the latter is 

 bounded, above and to the outside, by a 

 broad groove for the lateral sinus, which 

 groove passes from the occipital bone to the 

 mastoid angle of the parietal, from thence to 

 the mastoid process of the temporal (where 

 the mastoid foramen opens into it), and, ulti- 

 mately, to the occipital bone again, where it 

 turns forwards to the foramen lacerum pos- 

 terius. In this groove is seen the termination of 

 the lambdoidal suture, and the additamentum 

 suturae squamosae and the additamentum su- 

 turae lambdoidalis cross it; the principal 

 portion of the latter being seen in the cere- 

 bellar fossa. Anteriorly, and above the fora- 

 men lacerum posterius, is the cerebellar surface 

 of the petrous process of the temporal bone ; 

 exhibiting the openings of the meatus audi- 

 torius internus and of the aqueduct of the 

 vestibule ; and, on the ridge which separates 

 this from the cerebral surface, the groove for 

 the petrosal sinus. 



The calvaria possesses in its centre a dense 

 curved rib, which extends through the roof 

 from the anterior to the posterior part of the 

 base, but which is more evident at its extre- 

 mities than in its middle, where it is generally 

 marked by a groove for the longitudinal sinus. 

 The frontal spine commences it, and its ter- 

 mination is the superior limb of the internal 

 crucial spine ; the intermediate portion (where 

 it is masked) is the sagittal suture. On each 

 side, and from before backwards, we notice 

 in succession the frontal depression ; the coro- 

 nal suture ; the parietal depression, and several 

 arterial sulci running towards it from below ; 

 part of the lambdoidal suture; and, lastly, 

 the cerebral fossa of the occipital bone. On 

 each side of the sagittal suture are the fossae 

 Pacchioni, and, near its back part, the foramen 

 parietale. 



A comparison of the external and internal 

 surfaces of the cranium establishes the fact 

 that there is a general correspondence of the 

 two as far as regards those parts which are in 

 contact with the periphery of the brain. But, 

 between the several divisions of that organ, 

 there are developed on the inside of the skull 

 very large ribs and processes which destroy the 

 particular correspondence of the two surfaces. 



