CHAP, in.] SKELETOX OF THE HEAD AXD TBUNK. 87 



two ftbro-cartilaginoiis disks (inter-articular fibro-cartilagcs) arc inter- 

 posed between tlic two articular surfaces. Motion is facilitated by 

 three separate S3'novial membranes ; one between the disks, one 

 between the upper disk and the glenoid surface, and the third between 

 the lower disk and the condyloid surface. 



The mpsnht}' ligaincnt is a librous membrane which surrounds 

 the articulation just mentioned, its fibres passing from the circum- 

 ference of the glenoid surface to the condyle. It adheres to the 

 margins of the interposed fibro-cartilaginous disks, and it is 

 strengthened on its inner and outer sides by certain accessory fibres 

 which might be distinguished respectively as internal and external 

 lateral ligaments. 



The stijlo-nmxillanj lUjmnent arises mainly from behind, but 

 partly from in front of the margin of the meatus auditorius externus. 

 It passes to the angle of the mandible. 



It gives attachment, on its inner side, to some of the fibres of the 

 internal pterygoid muscle. The stylo-glossus is attached to its 

 upper surface, while its exterior is connected with the masseter. 



A thin interarticular cartilage is interposed between the anterior 

 marf^ins of the two horizontal rami of the mandible. 



Another cranial ligament which it may be well to mention, is 

 the jjost-orhital ligament which connects the apex of the post-orbital 

 process of the malar with the apex of the adjacent post-orbital 

 process of the frontal. 



§ 41. Having now completed our survey of the parts which make 

 up the cranial division of the cat's axial endo-skeleton, the most 

 generalized view of them at present attainable may, perhaps, be 

 expressed as follows : — 



The skull consists of a central axis, made up of the basi- occipital, 

 basi- sphenoid, and pre-sphenoid, and which axis is continued on 

 forwards by the median ethmoid. 



To this central axis ascending and descending arches are annexed, 

 having certain other structures intercalated between the former. 

 Thus we have an occipital arch completed by the basi-occipital, 

 ex-occipitals, and supra-occipital. 



Secondly, we have a posterior sphenoidal arch, completed by the 

 ali-sphenoids and parietals. 



Thirdly, we have an anterior splienoidal arch, completed by the 

 orbito-sphenoids and the frontals. These three arches embrace the 

 brain, ■which is the enlarged anterior continuation of the spinal 

 marrow and forms the anterior termination of the nervous centres. 

 On this account these arches may be termed " neural," like the 

 vertebral arches which similarly enclose the spinal marrow. 



The most anterior, or anterior sphenoidal arch, is open in front, 

 the bone of the olfactory organ (the ethmoid) being, as it were, 

 thrust into the aperture which is left by it. 



Into the gap left on each side between the ex-occipital and the 

 aH-sphenoid, the auditory organ (the temporal bone) is thrust. 



Similarly, the very much smaller gap left between the ali- and 



