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 symphysis. 



Fig. 338.-Head and neck of a human embryo 18 weeks old with the vuceral skeleton exposed; 

 after KOLLIKEK. 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 annulus tympanicus is visible. 



ha, Malleus, which passes uninterruptedly into MECKEL'S cartilage, MK ; uk, bony lower jaw 

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

 st, shapes ; pr, annulus tympanicus ; grf, processiu styloideus ; Isth, ligamentuni stylo- 

 hyoidxim ; kh, lesser oornu of the hyoid bone ; gh, its greater cornn. 



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 cf 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 tlie jaw 

 between palato-quadratum and os articulave. 



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



40 



