THE SKELETON 65 



through [an interspace between the elements of the auditory 

 region of the skull, known as] the Glaserian fissure. 



The second visceral or primitive skeletal arch (II, Fig. 45) 

 becomes, in Man, proximally connected with the auditory capsule ; 

 distally it becomes related to the next arch behind (III of Fig.). 

 Its intervening portion, which at first is cartilaginous, may 

 become partly or altogether ossified, but it is usuall} 7 - transformed 



FIG. 45. HEAD OF A HUMAN EMBRYO OF THE FOURTH MONTH. Dissected to show the 

 auditory ossicles, tympanic ring, and Meckel's cartilage, with the hyoid and thyroid 

 apparatus. All these parts are delineated on a larger scale than the rest of the skull. 



ml., malleus; in., incus; st. , stapes ; an., tympanic ring ; tp., tympanum ; I (mk. ), first 

 skeletal (mandibular) arch (Meckel's cartilage) ; II, second skeletal (hyoid) arch ; 

 III, third (first branchial) arch; IV, V, fourth and fifth arches (thyroid cartilage); 

 b. hy., basihyal element ; tr., trachea ; md., bony mandible. 



along the greater part of its length into a fibrous band. 



In other cases it is replaced by a series of small cartilaginous 

 or osseous bodies which form a chain, recalling the arrangement 

 existing in many lower Mammals. The proximal end of 

 this arch becomes, in Man, the very variable styloid process of 

 the temporal bone ; the distal end, on the other hand, forms the 

 lesser cornu of the hyoid. This latter bone (the hyoid) also con- 

 sists of a central portion or body (&.%.), and a larger or posterior 



