DEVELOPMENT OF THE FACE. 957 



skull, a superior arcli is connected, composed of bones analogous to the laini- 

 11 re and spines of the vertebra?, and, like them, inclosing and protecting the 

 nervous mass within. The formation of the superior arch in connection with 

 the basi-occipital centre commences at an early period, by the appearance of 

 two additional ossifying points in the cartilage on either side of the foramen 

 magnum, which develop into the condyloid and lateral portions of the occip- 

 ital bone or ex-occipitals ; whilst the crown of the arch, or supra-occipital 

 bone, represented in the adult by the broad expanded plate, is formed by 

 two osseous points in cartilage, aud one or two in the membrane immediately 

 above the cartilage that subsequently coalesce. The upper arch of the basi- 

 sphenoid begins as a bony deposit iu the cartilage representing the great 

 wings of the sphenoid bone, or ali-sphenoids (i, Fig. 357) ; and the crown of 

 this arch, formed by the parietals, is exclusively produced, not by intra- 

 cartilaginous, but by intra-membranous ossification. A third upper arch is 

 connected with the pre-sphenoid by the ossification of the projections of the 

 pre-sphenoid (&), representing the alse miuores of the sphenoid or orbito- 

 sphenoids, the crown of this arch also, the frontal bone, developing by iiitra- 

 membrauous ossification, like the parietal and supra-occipital bones. The 

 most anterior of the centres of ossification that appears in the basal cartilage 

 of the skull, forms the lamina perpendicularis of the ethmoid (b, Fig. 358), 

 and is seen in vertical section in Fig. 358. At an early period the cartilage 

 sends out two processes, c, e, which inclose the nasal fossae. The superior 

 and middle turbinals (opposite e) are developed as outgrowths from this car- 

 tilage. The inferior turbiual (/) is of later date. The nasal bones, d, d, 

 are developed as opercular bones in the membrane covering the primitive 

 cartilage, and overlie the nasal cartilage; whilst at the base of the cartilage, 

 but developed from membrane, is the vomer (a). The remaining bone 

 which enters into the formation of the skull is the Temporal, the develop- 

 ment of which, formerly much misunderstood, has been very carefully in- 

 vestigated by Prof. Huxley, Mr. Parker, and others ; from whose inquiries 

 it appears that the squamosal portion, like the parietal and frontal bones, is 

 developed from membrane. Below this, and developed from fibro-cartilage, 

 a ring of bone appears incomplete above, forming the auditory meatus, and 

 termed the tympanic bone. Finally, there are three centres of ossification, 

 for which Mr. Huxley proposes the terms, prootic, epiotic, and opistlwtic. The 

 prootic lies behind the foramen ovale, and forms the petrosal bone or petrous 

 portion of the temporal. The epiotic surmounts the posterior vertical semi- 

 circular canal, and forms the mastoid portion of the temporal ; whilst the 

 opisthotic is continuous with the ossification which primitively surrounds the 

 feuestra rotunda, and forms the floor of the Tympanum, lying in front of 

 the point of exit of the eighth pair of nerves. 



795. The development of the Face next claims our attention. It proceeds 

 from three parts, two of which are symmetrical and the third single. The 

 former are the first pair of visceral arches (a, Fig. 359), sometimes termed 

 the mandibular arch, from which the superior maxillary process is budded 

 off on each side. The asymmetrical part is the frontal process, with its alee 

 or internal nasal processes (seen on each side of nf, Fig. 360), the develop- 

 ment of which into the turbinals, covered by the nasals, has been already 

 alluded to. The two lateral halves of the first visceral arch (1, Fig. 359) 

 uniting in the middle line, form the rudiment of the lower jaw, and origi- 

 nally consist of two parts oil each side, one of which, the inferior maxillary 

 process, is cartilaginous, and becomes converted at its base into the malleus 

 (b, Fig. 361), whilst its distal portion is prolonged downwards and forwards 

 in the form of a slender rod, known under the name of Meckel's Cartilage, 

 on the outer side of which the lower jaw (d) is developed as a splint bone. 



