502 DR. J. MUEIE ON THE ANATOMY OF THE SEA-LION. 



behind. The second, orbito-frontal or middle region is chiefly formed by the orbit 

 itself. It embraces, moreover, a portion of the vacuity of the temporal fossa, externally 

 is guarded by the malar arch, is bounded above by the frontal bone and supraorbital 

 process, and below and within is defined by the pterygopalatine wall. Its length is 

 almost an exact third of the long diameter of the cranium. 



These two anterior segments or provisional boundaries together comprise the facial 

 region, which here bears a proportion to the entire length of the skull as 6 is to 10. 

 The third, hinder and largest segment, the temporo-occipital, is nearly as deep as it is 

 long, and it thus has a marked rectangular configuration. 



The upper cranial surface exhibits even more definitely the three regions just spoken 

 of. That portion containing the brain is broad, and more particularly so at the exoc- 

 cipitals. The frontals are deeply scooped out opposite the zygomatic arch ; and this 

 narrowing contrasts with the prominent postorbital processes. Each malar arch has an 

 external flattened aspect, and only slightly veers inwards anteriorly. At the maxillary 

 bones the skull is narrower ; and quite in front these and the premaxillse form an un- 

 evenly rounded muzzle; four bosses (see fig. 1) indicate the relative positions of the 

 outer incisors and canine teeth. 



b. The Cranial Bones. — Anfractuous low ridges chiefly indicate the occipital elements, 

 which otherwise are more or less coalesced. The basiocciput inferiorly is somewhat 

 oblong in shape, and rather longer from before backwards than across ; the foramen 

 magnum is nearly circular in figure. The condyles form, posterior to the opening, an 

 inferior projecting and thickened semilune of bone; but the upper margin of the 

 foramen magnum, composed of the inferior hinder border of the supraoccipital, is 

 thin. A large exoccipital canal 1 , or condyloid foramen, pierces the bone just within 

 the articulating surface. The supraoccipital forms a well-defined arch, bounded by a 

 broad moderately raised lambdoidal crest. The surface of the supraocciput is very 

 uneven, being marked mesially by a sharp crest, on either side of which are deep 

 hollows for the nuchal muscles. 



The parietals are narrow, flat-topped, and short ; suturally they are firmly connected 

 with each other, and interossified with the squamous portion of the temporals. The 

 squamous element of the temporal bone is broad and flat. The mastoidal surface is 

 rather prominently ridged just behind the external auditory meatus, or with a moderate- 

 sized paramastoid process; rearwards it is sunk flat, and joins a narrow, scarcely appre- 

 ciable paroccipital process. The tympanic bone is fair-sized, but not inflate. It is 

 directed obliquely inwards, backwards, and downwards, ending in a sharp margin ; 

 superficially (■/. e. inferiorly) it is broadly grooved and indented on its inner face. A 

 slight ridge is all that indicates a styloid process ; but there is a short tooth-like cusp 

 projecting forwards in front of the tympanic, and overlooking the carotid foramen. 

 The glenoideum is narrow antero-posteriorly, but broad transversely, and moderately 

 1 A term proposed by Mr. H. N. Turner, see P. Z. S. 1848, p. 75. 



