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 usually transformed 
SSS SS OSS 
= <—— <> 
SS == 
1 
1} 
Fic. 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 (mA.), 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 ; d7., 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 (b.hy.), and a larger or posterior 
F 
