189S.] OSTEOLOGY OF THE IMPENNES. 963 



lambdoidal ridge across the top of the skull to join the apex of the 

 fossa of the opposite side (PI. LIX. fig. 5, t.l.r.). In Splieniscus 

 the posterior region of the fossa becomes greatly deepened, and 

 the squamoso-parietal wings appear as though they had been 

 forced backwards on to the cerebellar dome, leaviug a deep groove 

 between the base of this and the cerebral dome (PI. LIX. fig. 1). 

 As already stated, the fossa of one side is separated from that of 

 its fellow on the other by a median, dorsal, sagittal ridge. The 

 lambdoidal ridge of C'atarrhactes is represented here by the free 

 edge of the huge squamoso-parietal wing : in addition, there 

 exists a second ridge anterior to this — the coronal ridge already 

 described (p. 961), which is connected with the lambdoidal by a 

 median sagittal crest (PI. LIX. fig. 5, cor.r.). These ridges serve 

 for the attachment of the peripheral portion of the temporalis 

 muscle. The squamosal and parietal bones only take part in the 

 formation of the temporal fossse. The posterior region of the 

 temporal fossa is wider in C. chri/solojyJtus than in C. chriisocome, 

 that of C. sclilegeli is wider still. In Meriadiiptes antipoclum it 

 reaches its maximum, being both wide and deep, and somewhat 

 closely resembles that of Eudyptula. The squamoso-parietal 

 wings on either side are well developed and curve gently backwards, 

 the outline of the free edge corresponding with that of the curve 

 of the cerebral dome. 



In Aptenodytes this region of the fossa is exceedingly shallow. 

 In Eudyptula it is intermediate between the typical Catarrhactes 

 and Splieniscus ; that of E. alhosignata reaches the lambdoidal 

 ridge, in E. minor it falls below this. 



The trigeminal foramen lies near the base of the skull, shghtly 

 below the level and mesiad of the articular head of the quadrate. 

 Immediately above this, to the inner side of the squamosal 

 prominence, is a tubular recess lying between the prootic and 

 alisphenoid bones, and leading eventually, in the dried skull, into 

 the cranial cavity. This recess is apparently derived by an 

 invagination or ingrowing of the alisphenoidal border of the 

 mouth of a fenestra lying immediately above the trigeminal 

 foramen, with which it may even bo confluent, as in the case of a 

 young, macerated skull. It is found also in the skulls of the 

 Tubinares — in some of which it is of great size — and Stegano- 

 podes (15). 



The 01'bit is overarched, behind and above, by the postorbital 

 process and supra-orbital ledge. The latter has already been 

 described (p. 961 ) ; the former is made up in part of a lateral 

 expansion of the frontal, and in part by the alisphenoid, to which 

 is added a separate element in the shape of a cartilagiuous 

 sphenotic. Later the whole fuses into an indistinguishable out- 

 standing mass — the postorbital process (Pis. LX., LXI. figs. 2 

 & 3). The inner wall of the orbit is formed for the most part by 

 the orbito-sphenoid, its hinder wall is formed by the alisphenoid. 

 The interorbital septum divides it mesially from the chamber of 

 the opposite side. The septum is formed by the presphenoid and 



