734 



CRANIUM. 



the membrana tympani, in front, by a sulcus 

 which is situated on the border between the 

 cerebral and under surfaces, and passes back- 

 wards, between the petrous and squamous 

 portions as a canal (the canalis Eustachianus), 

 which is divided by a lamina of bone, called 

 the processus cochleariformis, into two parts, 

 the inferior of which contains the Eustachian 

 tube, and the superior the tensor membranae 

 tympani muscle. Immediately behind the 

 fossa jugularis there is a rough surface, for the 

 articulation of the jugular process of the occi- 

 pital bone ; and to the outer side of this sur- 

 face is the foramen stylo-mastoideum for the 

 exit of the facial nerve. In front of and close 

 to this foramen, and between it and the jugular 

 fossa, is the long pointed process (the styloid 

 process) for the attachment of the stylo-maxil- 

 lary and stylo-hyoid ligaments, and the stylo- 

 pharyngeus, stylo-glossus and stylo-hyoideus 

 muscles; this process is embraced on the 

 outer side at its root by a portion of the ridge 

 separating the parotid and jugular fossae ; that 

 portion is called the vaginal process. In front 

 of the fossa jugularis are two foramina ; one 

 very large, the foramen caroticum ; the other 

 very small, to the inner side of the former and 

 nearly on the margin between this and the 

 cerebellic surfaces, being the termination of the 

 aqueduct of the cochlea. The foramen caro- 

 ticum is the inferior opening of the canalis 

 caroticus, a canal which exists in the bone, 

 and consists of two parts that are at right 

 angles with each other the inferior, short, 

 vertical, and extending upwards from the fo- 

 ramen caroticum into the substance of the 

 bone; the superior, horizontal, running length- 

 wise, and extending to the end of the petrous 

 process : in this canal there pass the carotid 

 artery to the cavity of the cranium, and a 

 filament of the nervus abducens, as well as 

 one of the Vidian, to the neck. A rough sur- 

 face is observed anterior to the foramen caro- 

 ticum for the attachment of the levator palati 

 and the tensor tympani muscles. 



The outer and posterior extremity of the 

 petrous is confounded with the mastoid and 

 squamous portions ; the inner and anterior is 

 open, and the bone is so much removed at its 

 upper part (to allow the carotid artery to pass 

 upon the body of the sphenoid) that it there 

 appears more like a deep groove than a tube. 

 This is filled up in the recent subject by a 

 plate of cartilage, but in the dried skull, when 

 this cartilage has been removed, there is found 

 an opening, between the sphenoid bone and 

 this extremity of the temporal, which is called 

 the foramen lacerum anticum. 



The mastoid portion is situated at the outer 

 end of the petrous, and behind and below the 

 squamous. It is of a nipple-like shape, with 

 an upper horizontal denticulated border, with 

 which the posterior inferior angle of the pari- 

 etal bone articulates ; and with a posterior semi- 

 circular border which is joined to the occipital : 

 in both directions it is overlapped by the bones 

 to which it is joined, except at the lower part, 

 where it is applied to the occipital by a sort 

 of harmonic suture. 



On its inner surface there is a deep, semi- 

 circular sulcus (the concavity looking back- 

 wards) which traverses its entire length ; it 

 receives the lateral sinus from the parietal bone 

 and transmits it to the lower part of the occi- 

 pital : there is generally observed in it a fo- 

 ramen (the foramen mastoideum), through 

 which a vein of the scalp communicates with 

 the sinus. 



Its outer surface is roughened and gives 

 attachment to the sterno-cleido-mastoideus, 

 and sometimes to the trachelo-mastoideus ; it 

 terminates below in the mammillary eminence, 

 called the mastoid process, behind and to the 

 inner side of which are two grooves the one 

 nearest to the process (the sulcus digastricus) 

 very evident, for the attachment of the digas- 

 tricus ; the other nearly on the articulating edge 

 (sulcus occipitalis)j less distinct, for the occi- 

 pital artery. 



The squamous portion rises upwards from 

 the mastoid, and part of the outer border of 

 the petrous portions ; it has a semicircular mar- 

 gin which embraces the parietal and sphenoid 

 bones. 



Its internal surface, which is concave, con- 

 tributes to form the middle fossa of the cra- 

 nium, and exhibits strongly the depressions 

 and elevations which correspond to the con- 

 volutions of the brain, and to the spaces 

 between them. At its anterior part, and com- 

 mencing at the angle between it and the pe- 

 trous process, there is a groove which runs 

 upwards and divides into other grooves, some 

 of which pass backwards; these are formed 

 by the middle meningeal artery and its branches. 

 The external plate of its border is prolonged 

 upwards, in such a manner that this surface is 

 surmounted by a rough articulating line, of 

 considerable breadth, which is applied on the 

 outside of the parietal and partly on the sphe- 

 noid bone. 



The external surface is slightly convex, is 

 smooth, and there may be often seen indica- 

 tions of deep branches of the temporal artery 

 having passed over it. It forms in part the 

 temporal fossa, and the temporal muscle is 

 attached to it. At its lower part, a process 

 (the zygomatic process) passes transversely 

 outwards, and is then twisted on itself in a di- 

 rection forwards, after the fashion of the ribs at 

 their angles ; so that the surface of the process 

 which would have been superior becomes 

 internal, and that which would have been in- 

 ferior becomes external. This process has 

 two roots, an anterior or transverse and a pos- 

 terior or longitudinal. The former is a convex 

 elongated eminence, situated transversely and 

 in front of a fossa (the fossa articularis), in 

 which the condyle of the lower jaw is placed. 

 This root is the eminentia articularis, on which 

 the condyle, with its inter-articular cartilage, is 

 thrown when the jaw is depressed. The pos- 

 terior root has itself two origins, which cir- 

 cumscribe the external auditory foramen ; 

 and it flows into and joins the anterior, just 

 when that root is altering its direction. Be- 

 tween the squamous process, and that part of 

 the zygomatic process which is between the 



