THE SKULL. 



485 



e.fr 



The incus is articulated with the quadrate end of the mandibular 

 arch, and its rounded head 

 conies in contact with the 

 stapes (fig. o4;'2, at) which 

 is segmented from the fe- 

 nestra ovalis. 



The main arch of the 

 hyoid becomes divided into 

 a hypohyal (/<./) below and 

 a sf ylohyal (st ft ) above, and 

 also becomes articulated 

 with the basal element of 

 the arch behind (bh). 



In the course of further 

 development the Meckel- 

 ian part of the mandibular 



arch becomes enveloped in 



~ . , .^ IIG. 341. EMBRYO PIG, TWO-THIRDS OF AN INCH 



a superficial ossification LONG; ELEMENTS OF THE SKULL SEEN SOMEWHAT 



DIAGRAMMATIC-ALLY FROM BELOW. (From Parker. ) 



pa.c/t lie 



pa.cli. parachordal cartilage; nc. notochord; 

 au. auditory capsule ; py. pituitary body ; tr. tra- 

 beculse ; c.tr. trabecular cornu ; pn. prenatal car- 

 tilage ; e.n. external uasal opening ; ol. nasal cap- 

 sule ; p.pfl. palatopterygoid tract enclosed in the 

 maxillopalatine process; mn. mandibular arch; 

 /o/- hyoid arch; tli.li. first branchial arch; la. 

 facial nerve; 8. glossopharyngeal ; 86. vagus; 

 0. hypoglossal. 



t.tr 



forming the dentary. Its 

 upper end, adjoining the 

 quadrate region, becomes 

 calcified and then absorbed, 

 and its lower, with the ex- 

 ception of the extreme 

 point, is ossified and sub- 

 sequently incorporated in 

 the dentary. 



The quadrate region remains relatively stationary in growth as 

 compared with the adjacent parts of the skull, and finally ossifies to 

 form the malleus bone of the ear. The processus gracilis of the 

 malleus is the primitive 

 continuation into Meckel's 

 cartilage. 



The malleus and incus 

 are at first embedded in 

 the connective tissue ad- 

 joiningthe tympanic cavity 

 (hyomandibular cleft, vide 

 p. 435) ; and externally to 



them a bone known as the Flo 3i . 2 EMBRYO Plo> AN INCH AND A TH IHD 

 tympanic bone becomes de- LO NG ; SIDE VIEW OF MANDIBULAR AND HYOID ARCHES. 



THE MAIN HYOID ARCH IS SEEN AS DISPLACED BACK- 

 WARDS AFTER SEGMENTATION FROM THE INCUS. (From 



Parker.) 



tff. tongue ; ink. Meckelian cartilage ; ml. body 

 of malleus ; mb. manubrium or handle of the mal- 

 leus ; t.tij. tegmen tympani ; i. incus; st. stapes; 

 i.hy. interhyal ligament ; xt.h. stylohyal cartilage ; 

 i./i. hypohyal ; b.h. basibranchial ; tli.li. rudiment 

 if first branchial arcli ; In. facial nerve. 



h.h 



th.h 



veloped so that they be- 

 come placed between the 

 tympanic bone and the 

 periotic capsule. In late 

 foetal life they become 

 transported completely 

 within the tympanic cav- 



i. 



h.l 

 of 



