134 



THE SKELETON. 



Occipital. 

 Two Parietal. 



Cranium. 8 forces. / m ron r p ' 



jTwo Temporal. 



[Sphenoid. 

 \Ethmoid. 



Skull, 22 bones. Two Nasal. 



Two Superior Maxillary. 

 Two Lachrymal. 

 Two Malar. 

 Face, 14 bones. Two Palate. 



Two Inferior Turbinated. 



Vomer. 



Inferior Maxillary. 



BONES OF THE CRANIUM. 

 THE OCCIPITAL BONE. 



The Occipital Bone (Fig. 89) is situated at the back part and base of the 

 cranium, is trapezoid in form, curved upon itself, and presents for examination 

 two surfaces, four borders, and four angles. 



The External /Surface is convex. Midway between the summit of the bone 

 and the posterior margin of the foramen magnum is a prominent tubercle, the 

 external occipital protuberance, for the attachment of the Ligamentum NuchaB ; 

 and descending from it as far as the foramen, a vertical ridge, the external 

 occipital crest. This tubercle and crest vary in prominence in different skulls. 

 Passing outwards from the occipital protuberance on each side are two semi- 

 circular ridges, the superior curved lines ; and running parallel with these from 

 the middle of the crest, are the two inferior curved lines. The surface of the 

 bone above the superior curved lines is smooth on each side, and, in the recent 

 state, is covered by the Occipito-frontalis muscle, whilst the ridges, as well as 

 the surface of the bone between them, serve for the attachment of numerous 

 muscles. The superior curved line gives attachment internally to the Trapezius, 

 externally to the Occipito-frontalis and Sterno cleido-mastoid, to the extent 

 shown in Fig. 89 ; the depressions between the curved lines to the Complexus 

 internally, the Splenius Capitis and Obliquus Capitis Superior externally. The 

 inferior curved line, and the depressions below it, afford insertion to the Rectus 

 Capitis Posticus Major and Rectus Capitis Posticus Minor muscles. 



The foramen magnum is a large oval aperture, its long diameter extending 

 from before backwards. It transmits the spinal cord and its membranes, the 

 spinal accessory nerves, and the vertebral arteries. Its back part is wide for 

 the transmission of the cord, and the corresponding margin rough for the 

 attachment of the dura mater inclosing the cord ; the forepart is narrower, being 

 encroached upon by the condyles; it has projecting towards it from below the 

 odontoid process, and its margins are smooth and bevelled internally to support 

 the medulla oblongata. On each side of the foramen magnum are the condyles, 

 for articulation with the atlas ; they are convex, oblong, or reniform in shape, 

 and directed downwards and outwards; they converge in front, and encroach 

 slightly upon the anterior segment of the foramen. On the inner border of 

 each condyle is a rough tubercle for the attachment of the ligaments (check) 

 which connect this bone with the odontoid process of the axis; whilst external 

 to them is a rough tubercular prominence, the transverse or jugular process 

 (the representative of the transverse process of a vertebra) channelled in front 

 by a deep notch, which forms part of the jugular foramen. The under surface 

 of this process affords attachment to the Rectus Capitis Lateralis; its upper or 

 cerebral surface presents a deep groove which lodges part of the lateral sinus, 



