THE ORGANS OF THE INTERMEDIATE LAYER OR MESENCHYME. 625 



bone, which makes its appearance in the articular part of the 

 cartilage and produces the os articulare, is a primary bone. With 

 this are associated several covering bones arising in the surrounding 

 connective tissue, two of which, the angulare and the dentale, 

 acquire special importance. Both are attached to the outer 

 surface of the cartilaginous [Meckelian] rod, the angulare near the 

 joint, the dentale in front of it and extending to the syrnphysis. 



Jut 



III,! 



uk 



MK 



1"' 



Fig. 338. Head and neck of a human embryo 18 weeks old with the visceral skeleton exposed, 



after KOLLIKF.R. Magnified. 

 The lower jaw is somewhat depressed in order to show MECKEL'S cartilage, which extends to the 



malleus. The tympanic membrane is removed and the annnlns tympaiiicus is visible. 

 lie, Malleus, which passes uninterruptedly into M ECKEL'S cartilage, A/A" ; ulc, bony lower jaw 



(dentale), with its condyloid pmcess articulating with the temporal bone; am, incus; 



st, stapes; pr, aunulus tympaiiicus; grf, processus styloidens ; lath, ligamentnm stylo- 



liyoideum ; kh, lesser cornu of the hyoid bone ; t/h, its greater cornu. 



The latter is an important skeletal element, which attains a consider- 

 able size, receives into its upper margin the teeth, and grows around 

 the cartilage of MECKEL in such a manner that the cartilage is almost 

 completely enclosed in a bony cylinder. The whole complicated 

 apparatus, composed of several bones and the original cartilage 

 enclosed within them, articulates at the primary joint of the jaio 

 between palato-quadratum and os articulare. 



The same fundaments are again met with in Mammals and Man. 



40 



