SKELETON*. 



SKELETON. 



the orbital iuxhe or ridges, and they form the front and prominent 

 part of the orbiU. The notch (2) a named the naul notch ; on 

 either title of it are fixed parts of the upper jaw, and in the middle 

 the nasal bone*, which rest behind ou a process called the nasal 

 pine (3). At the outer extremity of each orbital arch U the 

 external angular process (4,4), and at the inner extremity the internal 

 .ngiiUr process (5, 5) ; the former is articulated with the malar, the 

 latter with the upper jaw and lachrymal bones. Near the ir.ternal 

 process is the Supra-Orbital Foramen, or notch (0, 0), through which 

 the frontal Teasels and nerve pan from the orbit to the forehead. 

 Just above it, and by its side, is a rounded elevation, the frontal pro- 

 tuberance (7), which marks the situation of the subjacent frontal 

 sinuses, air-cavities, between the two layers of which the bone is 

 composed. They vary much in size in different persons, and com- 

 municate with the interior of the nose. On either side of the middle 

 line, and extending above the orbital ridge, the surface of the bone U 

 again elevated in the superciliary ridge (8, 8), an arched prominence 

 behind the eyebrow. The rest of this anterior surface is smooth and 

 even, but in different persons its form is as varied as that of any 

 other feature. Ou either side it terminates rather abruptly with a 

 curved border (9), which forms the front boundary of the temporal 

 fossa (10), and behind which there is a smooth surface, to which the 

 fore part of the temporal muscle is attached. 



The posterior or cerebral surface of the Frontal bone (fy. 12, !>) is 

 concave. Along the middle line there is a broad groove (1), in which 

 a part of the longitudinal sinus [BRAIN] lies ; and at the fore and 



iff. U. 



4.4 



lower end of this a ridge, to which a process of dura mater called the 

 Falx U attached. The ridge ends at a hole named the Foramen 

 CaDCum. The rest of this surface in marked by depressions and 

 ridges fitting to the convolutions of the surface of the brain. 



The orbital portions (';, 3, 8) of the frontal bone are thin plates 

 extending almost horizontally backwards from the orbital arclies. 

 Between their inner borders is a space, the ethmoid notch, into which 

 fie ethmoid bone fits, and just anterior tn which are the apertures 

 (4, 4) leading into the frontal sinuses. The under surface of each 

 plato U concave, smooth, and even ; and has nt its outer and fore part 

 a shallow depression, in which the lachrymal gland is lodged, and at 

 iU inner and fore part a mark to which the pulley of the trochlcaris 

 muscle of the eye is attached. The upper surface U marked in corre- 

 spondenre with the irregularities of the under part of the anterior 

 lobe of the brain, which rests upon it. 



The posterior and upper margin of the frontal bone (o, 6, 5) is 

 joined by the coronal suture to the two parietal bones ; and it is cut 

 obliquely in such a manner that iU edges rest upon theirs above, and 

 theirs overlap its below. The lower part of this margin is covered by 

 the ate of the sphenoid, where they rise into the temporal fossio. 

 The frontal U uiunlly in the adult only a single bone, composed (as all 

 the bones in the middle plane of the skeleton are) of two equal and 

 similar halves : these are developed separately, and they sometimes 

 remain undivided by a continuation of the sagittal suture which 

 passes from between the two parietal straight down the middle of the 

 '. :. 



The construction of the Parietal Hones, which form all the upper 

 and middle part of the skull, i.i very simple. In fg. 13, at a the 



exterior, and at 4 the interior, of the right parietal is represented. 

 They are quadrilateral, and of nearly equal thickness throughout 

 The outer convex surface is everywhere smooth, except at its lower 

 border (1), where it is overlapped by the temporal bone in the 

 squamous suture, and just above this part, where there is a slight 

 arched ridge (2) for the attachment of a portion of the teiupor.il 



rig. is. 



muscle. The inner concave surface has impressions of the cerebral 

 convolutions, and a deep branching groove, which, beginning at the 

 fore and lower angle (3), thence ramifies diffusely. It lodges the 

 middle meniugeal artery of the dura mater. [BiiAis.] Along the 

 upper border is a broad shallow groove (4), which lodges part of the 

 longitudinal sinus, and is continuous with that on the interior of the 

 frontal bone. The borders of the parietal bones are all, except the 

 lower, deeply and irregularly indented ; and by the dove-tailing of 

 such irregular teeth they form, with the frontal bone in front, the 

 coronal suture, with the occipital behind, the lamboidal, and, in the 

 middle line at their own meeting, the sagittal. 



The Temporal Bones (jig. 14, as seen from without) are placed iu 

 the middle, lateral, and inferior parts of the skull. They present 

 each three distinguishable parts, which in the foetus are separated 

 namely, a Squamous portion (1), which forms the middle of the side 

 of the skull ; a Mostoid portion (2), which forms the thick pro- 

 tuberance that may be felt behind the ear; ami a ivtruus portion 

 (not visible in fig. 14, but iufg. 11 marked c), which passes from the 

 lower part of the squamous forwards and inwards in the base of the 



Fig. M. 



.-I. nil. The squomous bone or portion has a roundish form. Its u|ip<-r 

 edge covers iu the lower border of the parietal. Its exterior mirfuue is 

 smooth, and gives attachment to some of th< muscle. At 



the hinder part of iU lower border is nil oval aperture (3) leading tn 

 the Meatus Auditorium Externus [KAII], a jnnsage which goes forward* 

 and inwards to the tympanum in the interior of the petrous portion. 

 Immediately anterior to this, and under the fore part of the bone, is 

 the Oleuoid Cavity (4), a deep transversely oval hollow, with which 

 the coudyle of the lower jaw is articulated, and behind which is a 

 narrow chink, the Fissure Glascri, separating it from a strong ridge 

 which runs along the upper surface of the petrous bone. In front of 

 the gleuoid cavity is a prominence, which forms ils border, the Tuber 

 Articulare (5); and from its outer part there prut ntally 



forwards, as if springing from the tuber aad two other slightly 

 elevated lines running lack ward*, a long narrow portion of bone, the 

 Zygomatic Process (6), the enlarged end of which joins a short 

 process of the malar bone to form the Zygoma, an arch beneath 

 which the temporal muscle playo, and whose pizo and strength are 

 generally in direct proportion to those of that muscle, and to the 

 force with which the lower jaw in worked in gnashing with the teeth. 



