I08 COMPARATIVE MORPHOLOGY OF VERTEBRATES 



hyoid is continuous with the stapes; later it joins the otic capsule behind the 

 fenestra vestibuli, while ventrally it joins its fellow and is connected with the 

 first branchial arch by a median cartilage, probably the copula. 



In the adult the so-called facial bones are more closely related to the cranium 

 than in the lower groups, and distinct bones are fewer than in lower vertebrates, 

 the reduction being due in part to actual loss, in part to the fusion of elements 

 which elsewhere remain distinct. The obliteration of sutures has gone farther 

 in the monotremes and some of the carnivores and apes than elsewhere. Con- 

 nected with the loss of bones is the absence of the supratemporal arcade, but 

 the infratemporal bar consisting of processes from the squamosal and zygo- 

 matic (jugal or malar) is always present, bounding the single temporal fossa. 

 This may be separated from the orbit by a bar formed by zygomatic and frontal, 

 or the bar may be incomplete or absent so that orbit and fossa communicate. 



Fig. 114. — Median section of skull of young Erinaceus, after Parker, as, alisphe- 

 Doid; bo, basioccipital ; bs, otic bulla; crelh, cribiform plate of ethmoid; elhpp, perpen- 

 dicular plate of ethmoid;/, frontal; i7>, interparietal; tnx, maxillary; n, nasal; os, orbi- 

 tosphenoid; pi, palatine; pm, premaxillary; prs, presphenoid; pt, pterygoid; so. supraoc- 

 cipital; v, vomer; V^-XII, nerve exits; cartilage dotted. 



Usually the bones fuse in such a way that the complexes named on page 74 

 are readily recognized. The occipitalia are usually united into a single occipital 

 bone,'though the sutures between them may persist for some time. The basi- 

 occipital forms the so-called basilar process, while the exoccipitals bear the two 

 occipital condyles for articulation with the atlas. The exoccipitals may also 

 bear strong, ventrally directed, paramastoid (paroccipital) processes. The 

 membranous interparietal is sometimes distinct, sometimes fused to the supra- 

 occipital, though it may unite with the parietals. 



The sphenoidalia form the sphenoid bone of human anatomy. Basi- and 

 presphenoid form a 'body' from which two pairs of 'wings' arise, the ali- 

 sphenoids being the greater, the orbitosphenoids the lesser wings. A pair of 

 pterygoid processes are given off from the ventral side of the body and a part 

 of these in some cases persist as distinct pterygoid bones, but apparently are 

 not homologous with some of the elements of the same name in the lower 

 vertebrates since they are membrane bones. The equivalents of the pterygoids 

 of the non-mammals occur in the monotremes. A second pair of membrane 

 bones, the intertemporals, also belong to the sphenoid complex, fusing at an 

 early date with the dorsal margin of the alisphenoids. 



