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



derance. It occupies about half the total length, the other half being divided betwixt 

 the orbital region and the face proper or maxillo-premaxillary parts. The entire skull 

 is low, broad, and flat on the top. Superiorly, from occiput to nasals, approaches an 

 equal-sided triangle. The breadth of the mid frontals is not only relatively but abso- 

 lutely a trifle gi'eater than in the aged animal. On the other hand, the prefi-ontal pro- 

 cesses scarcely extrude. The jugals have but slight arching. The occiput is altogether 

 full, fiat, and vertical ; the condyles project little. Premaxillse comparatively short and 

 high ; spheno-orbital vacuity shallow, height proportionally great to length. Palate 

 shallow and short. Basioccipital and sphenoid parts smooth, and all other processes 

 small. Mandible with shallow shelving symphysis ; a wide ramal arch ; condyle short- 

 necked and low-set. 



Second stage. In this cranium, authenticated as a yearlmg, there is a sensible change 

 of cerebral to facial and prefrontal areas. Maxillae and premaxillse begin to lengthen. 

 Mid frontals narrow relatively to increase of prefrontal processes. The brain-region 

 becomes somewhat quadrangular; occiput rougher and begins to shoot backwards. 

 Temporal groove deepens ; jugal arch increases. The permanent teeth in place give 

 more character to the mouth ; lengthening and deepening of palate obvious ; the 

 hamular processes approach. Eminences of spheno-occipital and other regions show 

 indications of growth, but are not prominent. Condyles and coronoid processes of 

 lower jaw exhibit a tendency to vertical elevation ; mental portion of symphysis inclined 

 to become tuberose. 



Third stage. Face, orbito-frontal, and brain-division now bear more equal propor- 

 tion ; that is, the two former have increased in a greater ratio than the latter. The 

 mid frontals appear more scooped by reason of prefrontal development. By elongation 

 of condyles and concomitant increase of basi- and exoccipitals, the occiput acquires a 

 reverse obliquity to the flrst stage. The outline of the brain-cavity remains in abeyance, 

 whilst temporal and occipital crests become apparent, though yet moderate. Mastoid 

 and preoccipital eminences acquire a certain prominence. Orbito-jugal arch wider ; 

 premaxillae decidedly elongate. Teeth, especially canines, enlarged. Palatal grooving 

 deepened, the pterygoid processes nearing, hence postnares less open. Muscular im- 

 pressions on basioccipital well scooped, basiocciput turning upwards behind. Symphysis 

 lengthened ; upward tilt of ascending ramus. In this stage sexual distinction becomes 

 evident, although there is still considerable resemblance between them. 



Foiu'th stage. Here the changes become very notable. The excessive growth of the 

 canines of the male produce rounder, fuller premaxillae. Brain-expansion is arrested. 

 Mid-frontal width retrogrades, while prefrontal progresses. The jugal arch expands, 

 its orbital segment deepens, its post upper angle rises; the maxillary surface of orbit 

 gets fuller. Parieto-occipital crests and processes acquii'e importance ; and this causes 

 the after part of the top of the skull to be elevated and no longer smooth and broad. 

 Moreover on each side, at the fronto-parietal suture, bony projections appear. Arching 



