SKELETON. 



99 



the orbitosphenoid to a cartilage plate developed on the otic capsule. The ethmoid 

 parts are complicated, consisting of the two nasal capsules, the septum between 

 them, and, on the inside, coiled turbinal cartilages to support the olfactory membrane. 



Some of the visceral arches have been mentioned in speaking of the ear bones 

 (p. 74). The pterygoid cartilage is apparently lacking, and there is nothing that 

 can be interpreted as a quadrate except the incus. Meckel's cartilage extends for- 

 ward from the incus to the tip of the jaw. In the procartilage stage the hyoid is 

 continuous with the stapes; later it joins the otic capsule behind the fenestra ves- 

 tibuli, while ventrally it joins its fellow and is connected with the first branch- 

 ial 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 



FIG. 103. Diagram of the bones of the mammalian skull, altered from Flower. Cartilage 

 bones dotted, membrane bones lined; 2-12, nerve exits. 



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

 the monotremes and some of the carnivores and apes than elsewhere. Connected 

 with the loss of bones is the absence of the supratemporal arcade, but the infra- 

 temporal bar consisting of processes from the squamosal and zygomatic (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 in- 

 complete or absent so that orbit and fossa are one. 



Usually the bones fuse in such a way that the complexes named on page 66 are 

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

 though the sutures between them may persist for some time. The basioccipital 

 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 processes (paroccipital). The membranous 

 interparietal is sometimes distinct, sometimes fused to the supraoccipital, though it 

 may unite with the parietals. 



