620 



CnORBATA. 



thorn. In the floor of the cranium the sphenoid bone lies in front 

 of tlie basioccipital portion of the occipital. In many mammals 

 this consists of an anterior and a posterior portion throughout life; 

 in man this condition occurs at least in the embryo. Each of 

 these j)arts in development consists of three elements, the posterior 

 of the basisphenoid as the body, and the paired alisi^henoids (great 

 wings); the anterior is similarly composed of the presjihenoid and 

 the paired orbitosphenoids (lesser wings) (fig. 502, tipl, Ps, Ah, 

 Ors). In front of the sphenoid lies the ethmoid, Eth, likewise 

 formed from three parts, the mesethmoid, which forms a partition 

 between the two nasal cavities, and the ptaired ectethmoids, which 

 form the lateral walls of the nasal cavities. These last have com- 



Fio. 6i7. — Sknll of embryo Tatu^in. (After Parker, from 'Wiedersheim.) Cartilage 

 dotted, membrane and membrane bones lined, if, incus (quadrate): iJc, dentary; 

 f)\ frontal; /i, (above) membrane over anterior fontanelle, (belo^v) liyoid bones; 

 ini, premaxillary; ,7i(, jugal (malar) ; kh, remnants of e:ill arch: ^7, lachrymal: 

 /n/f, Meckel's cartilage: ;n.r. maxillary: ?i, malleus (articulare): no. nasal: <', oc- 

 cipital cartilage: o.s\ supraoccipital: jta, parietaUjJc, petrosal : y*/, squamosal : sf, 

 stapes: i)f, tympanic. 



plicated folds on their inner surface, the superior and middle 

 turbinated bones, which support the olfactory membrane, thus 

 greatly increasing its surface. With these is associated the os tur- 

 binale, a distinct bone, the inferior turbinated bone of human 

 anatomy. 



The temporal bone, which is intercalated between the roof and 

 floor of the sknll, can only be understood l)y its embryonic rela- 

 tions and its connexion with the first and second visceral arches 

 (fig. (;47). Its centre is formed by the petrosal [pe], developed 

 in the walls of the otic ca.psule. to which, as elsewhere in the 

 vertebrates, are attached : (1) the cartilaginous jaw arches, the 

 quadrate (ii), and the numdibular (« and mk) ; (2) the cartilaginous 



